Revert "[CodeGen]Allow targets to use target specific COPY instructions for live range splitting"

And dependent commits.

Details in D150388.

This reverts commit 825b7f0c.
This reverts commit 7a98f084.
This reverts commit b4a62b1f.
This reverts commit b7836d85.

No conflicts in the code, few tests had conflicts in autogenerated CHECKs:
llvm/test/CodeGen/Thumb2/mve-float32regloops.ll
llvm/test/CodeGen/AMDGPU/fix-frame-reg-in-custom-csr-spills.ll

Reviewed By: alexfh

Differential Revision: https://reviews.llvm.org/D156381