What is the name for the process which turned "iced cream" into "ice cream"?

Solution 1:

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.

Solution 2:

I do not know if there is more specific term (probably there is), but for now I can offer

• morphological clipping, shortening or truncation
• specifically it is back clipping or apocope

in hope that it will bring you closer to the specific term that deals with dropping of -ed specifically.