Remove dependencies on 1-variant fallback

This is just a first pass, there are still more issues to tackle.
But after this we start getting errors about genrules which require
more work to resolve, so I'll handle them in a separate cl.

Bug: 372091092
Test: m nothing --no-skip-soong-tests
Change-Id: Ibf8f6bca699ff7c3232495ae7fa2666c967ba90b