RegUsageInfo: Cleanup; NFC

- Remove unnecessary anchor function
- Remove unnecessary override of getAnalysisUsage
- Use reference instead of pointers where things cannot be nullptr
- Use ArrayRef instead of std::vector where possible

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@337989 91177308-0d34-0410-b5e6-96231b3b80d8
6 files changed