RemoveCopyByCommutingDef doesn't need hasPHIKill().

Instead, let HasOtherReachingDefs() test for defs in B that overlap any
phi-defs in A as well.  This test is slightly different, but almost
identical.

A perfectly precise test would only check those phi-defs in A that are
reachable from AValNo.

llvm-svn: 139782