fs_mgr: Remove blatant references to retrofit dynamic partitions.

Note, we are removing code that handles non-DAP to DAP updates, as well
as runtime code for retrofit DAP devices. We are not removing code
needed to flash Pixel 3, or liblp's ability to inspect Pixel 3 super
images.

Bug: 406251416
Test: th
Change-Id: Id94fa4679a6071d39b590dc3c78bbaf43e1d1636