lib: drop ObjectChange, DiaObjectChangeLegacy

We've now ported all usage to DiaObjectChange direct
2 jobs for zbrown/object-change in 14 minutes and 29 seconds
latest
Status Job ID Name Coverage
  Test
passed #934712
flatpak
flatpak

00:14:29

passed #934713
win32-ps
msys2-mingw32

00:05:49