Auto merge of #77373 - jonas-schievink:rm-rf-copy-prop, r=oli-obk

Remove the old copy propagation pass

This pass was added a long time ago, and has not really seen much improvement since (apart from some great work in #76569 that unfortunately ran into preexisting soundness issues). It is slow and unsound, and we now have a destination propagation pass that performs a related optimization and could be extended.

Closes #36673
Closes #73717
Closes #76740

Author: bors