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

[David Green via llvm-commits]

https://github.com/davemgreen approved this pull request.

As far as I understand this will start creating "illegal" copies that are not themselves supported (they go from high dregs+subreg to sregs, which isn't a valid copy). They are turned back into p pair of copies later on though, so it doesn't seem to be an issue in practice. If you are happy with it working like that then I am happy to give this a go and we can see if it leads to issues elsewhere.

LGTM

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