[Hexagon] [NFC] Cleaning up unused classes.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@223845 91177308-0d34-0410-b5e6-96231b3b80d8
Remove redundant variable.

Tested by adding assert(LoopVectorPreHeader == VecPreheader) on LLVM
test suite and SPECs.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@223847 91177308-0d34-0410-b5e6-96231b3b80d8
IR: Metadata: Detect an RAUW recursion

Speculatively handle a recursion in
`GenericMDNode::handleChangedOperand()`.  I'm hoping this fixes the
failing hexagon bot [1].

[1]: http://lab.llvm.org:8011/builders/llvm-hexagon-elf/builds/13434

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@223849 91177308-0d34-0410-b5e6-96231b3b80d8