No, nothing official. You can make Intimidate checks but that's a poor substitute. I made a quick cut at a 3e morale system with two factors, aggression and morale, on my blog. There's not a lot of reason not to just use the old school morale system straight, though, it's not like you threw away all your d6's with the d20 system.
My contention is - not much if anything.
History. All D&D settings are full of things done by ancient wizards or whatnot that are not actually achievable by PCs or NPCs under the normal game rules, whether it's the Field of Maidens or the Mana Wastes in Golarion or the Sea of Dust in Greyhawk or everything in the Forgotten Realms and Eberron. Using E6 for your PCs doesn't change that at all, so you don't need to retcon history to only account for "sixth level abilities."
Politics, Civics. First check out What percentage of the population is magical in Pathfinder's world of Golarion? Golarion is designed to not have many high level NPCs in the first place. Only people like country leaders are listed as higher level, or super-rare exceptional NPCs like Baba Yaga. You don't actually have to use the E6 rules for NPCs, so you could keep the most notable high level folks as their real high level and just make them super dangerous to cross for E6 PCs - a foe to plan a campaign around, not a mob to grind once the party's high level. Or, you can limit those rulers to L6 and rebuild them (where relevant) using the E6 rules. In that case the only political change I can think of is in cases where humans are collaborating with nonhumans (with the giants and winter wolves in Irrisen for example), devising a more nuanced justification for their cooperation than "a high level caster would melt the giants' faces if they misbehaved." So no real politic or civic changes except challenging you to find more textured explanations than "He in charge cuz he can bash everyone else."
Economy. Economy wise, there's less to spend megagold on since there's not super expensive items - but the inflation and problems of PCs having megagold compared to normal folks isn't good or conducive to a coherent game world anyway (see How to handle wealthy player characters as a GM?). The Golarion economy works better without the "hey there's a guy with 100,000 gp worth of stuff on him" problem.
Military. No D&D setting has ever had their militaries really reflect the realities of the D&D magic and combat system. They're always medieval-based theories of troops and fortifications that fly, invisibility, etc. make hash of. So there's not much to "dumb down" - the most notable "fantasy" units in Golarion are things like the Sable Marines of Korvosa who ride hippogriffs, which is still completely appropriate for E6.
Bestiary. Obviously you'd take a lighter hand with the high CR monsters just like the E6 rules say, but you don't have to remove them all - so a Linnorm King having to defeat a Linnorm is still on the table, it just means that the Linnorm Kings are way more bad ass than just being "a high level guy."
Adventures. The main problem with E6, really, is using the adventure content for Golarion. The Adventure Paths all go way past 6th level and chapters 3-6 would require significant adaptation, including the encounter tables and all. Since a big draw of Pathfinder/Golarion is the adventures, that's really the major downside. Also, if you limit all NPCs to L6 then your capstone threats can only be "monsters," which removes legendary threats like Baba Yaga, which is a bad GMing mistake IMO.
Frankly, E6 makes Golarion make more baseline sense than the usual d20 rules do! That's a big part of its draw; Golarion like Greyhawk and most traditional D&D campaign worlds are really only coherent if you assume there's not a bumper crop of high level folks around.
Best Answer
In a word? No.
There are several people out there who have tried to cap 5e Character progression in differing ways (one such example being here), but there is no 'broadly accepted' system that I have ever seen.
Part of this is because 5E is much better balanced than 3.5E was. Yes, spellcasters are very powerful... but spells like Solid Fog that are basically "Be a Spellcaster or Lose" simply don't exist anymore. And the existence of spells like Solid Fog are the whole reason that E6 was invented in the first place. And other spells that 'broke things' at 7th level, such as Polymorph, received a significant Nerf. (Polymorph used to let you turn targets into dragons, aberrations, etc. Now it only lets you turn targets into Beasts)
See, 5E introduced Bounded Accuracy, sharply restricted the Magic Item creep, made non-casters more powerful than they used to be, and ditched a lot of the terribly unbalancing spells. These systemic changes are widely viewed by fans of the old E6 system as an integration of E6 design goals into the base system. As a result, it seems that the fanbase at large has not deemed the addition of an E6 system to be necessary. The opinion seems to be that 5E doesn't "break" at a certain level the way 3.5 did.
Advice Section
With the factual bit out of the way... let me offer a bit of advice.
If you want to cap character progression for your campaign, then do it. 5E provides rules for doing without XP, so your characters only advance at 'Milestones' (i.e. when the DM wants them to level up). So you could pace your entire adventure so that they level more slowly than 'normal' and only reach your chosen 'max level' by the time the campaign is over.
Alternately, have a look at Epic Boons in the DMG, and if you want to cap them at a particular level, but allow progression to continue... consider inventing some nerfed versions of those.
Bear in mind... 'Level 7' isn't quite as big of a deal in 5E at it was in 3.5. The 'Tiers' of adventure are divided up at...
As a result, in 5E... the published adventures tend to follow this trend.
Lost Mine of Phandelver deals in a fairly local threat, and caps out at level 5. Curse of Strahd deals with a Kingdom-scale threat, and caps out at level 10. Basically all the rest of them address threats that target an entire region, and cap at level 15.
So, just pace your game so that they level at a pace to keep them within the 'appropriate' range.