Revert "[SLPVectorizer] Add initial alternate opcode support for cast instructions. (REAPPLIED)"

This reverts commit r336812, which broke compilation of a number
of projects, see PR38154.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@336949 91177308-0d34-0410-b5e6-96231b3b80d8
2 files changed