Revert r139782, "RemoveCopyByCommutingDef doesn't need hasPHIKill()."
Revert r139782, "RemoveCopyByCommutingDef doesn't need hasPHIKill()."

It does, after all.

RemoveCopyByCommutingDef rewrites the uses of one particular value
number in A. It doesn't know how to rewrite phi uses, so there can't be
any.

git-svn-id: 0ff597fd157e6f4fc38580e8d64ab130330d2411@139787 91177308-0d34-0410-b5e6-96231b3b80d8

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