- Remove the previous check which broke coalescer-commute3.ll

- Remove the previous check which broke coalescer-commute3.ll
- For now, conservatively ignore copy MI whose source is a physical register. Commuting its def MI can cause a physical register live interval to be live through a loop (since we know it's live coming into the def MI).

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@47281 91177308-0d34-0410-b5e6-96231b3b80d8