Learn English – Is it still an “ice cream cone” if it doesn’t have ice cream

I don't think there is a specific term for the loss of -ed in these contexts. Rather, what you have is the interplay of a few different general trends.

The first factor is simply phonological. Iced cream, pronounced very deliberately, has a [stkr] cluster in the middle. In rapid speech, this is going to be reduced to [skr] anyway. The same is true of every other example you gave: if pronounced with the -ed, they contain difficult consonant clusters which are likely to be reduced in speech. This is known as elision.

The second factor is that English has a highly productive compounding process, which allows you to take any combination of two nouns and stick them together as a new lexical item. Once the phonological elision has taken place, it's immediately tempting to reanalyze the phonological string as a compound word rather than a noun phrase. So now ice cream is considered a single lexical item, and has the characteristic first-syllable stress of lexicalized compounds. This is a combination of reanalysis and compounding.

Makers of mass-produced dessert snacks in the United States struggled with this problem for years, a problem exacerbated in their case by the fact that the "cream-flavored cream" filling might in fact contain no cream. Their solution was to popularize terms such as "creme" and "creme-filled"—without the grave accent over the first e—and the even more heavily processed-sounding "kreme" and "kreme-filled." Dunkin' Donuts, for example, currently offers a Vanilla Kreme Filled Donut and a Boston Kreme Donut whose debt to any living cow (or kow) is unknown to me. A marketer might confidently claim that a wafer contained "cream-flavoured creme," without having to go into detail (on the front of the package, anyway) about what industrial substances made up the creme.

If you wanted to stay away from creme and kreme, the simplest way to avoid the repetition of cream in your example would be to replace the second cream with filling: "Wafers with cream-flavoured filling." In the context of a mass-produced sweet treat, U.S. readers would immediately interpret "filling" to mean "squishy or pasty (and very sugary) partially hydrogenated goo." But I don't know whether filling carries the same instantly recognizable sense outside the U.S. that it does here.