Update multiple flags to read-only

This updates the following flags to be read-only
 - zip_ng -> zip_ng_ro
 - desktop_file_handling -> desktop_file_handling_ro
 - visual_signals -> visual_signals_ro
 - hide_roots_on_desktop -> hide_roots_on_desktop_ro
 - use_peek_preview -> use_peek_preview_ro

It also removes the existing preupload check. Unfortunately this check
doesn't work on kotlin files so it's kind of only semi-useful.

Bug: 400475579
Test: m DocumentsUIGoogle
Flag: EXEMPT update flags to be read-only
Change-Id: I117a0e460beb488313ece178349058f5aa2e956e