enhance memcpy opt to turn memmoves into memcpy when the src/dest

enhance memcpy opt to turn memmoves into memcpy when the src/dest
don't alias.  Remove an old and poorly reduced testcase that fails
with this transform for reasons unrelated to the original test.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@80693 91177308-0d34-0410-b5e6-96231b3b80d8