[llvm] ARM: Remove override of shouldRewriteCopySrc (PR #125219)

[David Green via llvm-commits]

davemgreen wrote:

>From what I can tell if we peephole to these 'invalid' copies, like this patch does, the register coalescer will come along and add them in again. I'm not sure if that always happens though or whether it is worth combining them together, I haven't seen anywhere where this causes problems. Do you have a reason to remove this? The case I came up with where this did change things it made them better by removing some copies via gprs.

https://github.com/llvm/llvm-project/pull/125219