Miscompilation introduced by CopyPropagation

[tmiasko]

To reproduce the issue:

• Checkout 41dc394 (for reproducibility, but might be unnecessary).
• Enable copy propagation so that it runs on mir-opt-level=1.
• ./x.py test --stage 2 src/test/ui (disable incremental compilation, so that rustc is rebuild completely).
• Observe tests failures: "not all trait items implemented, missing ...".

[tmiasko]

The copy propagation incorrectly assumes that a use of a local in Operand::Move will not mutate it.

[jonas-schievink]

#72632 has landed now, so we could remove CopyPropagation and focus on that instead