[llvm] [LiveRegUnits] Enhanced the register liveness check (PR #66061)

[Christudasan Devadasan via llvm-commits]

cdevadas wrote:

This should be abandoned. Not sure why it is still open.
 We decided not to include `contains` in the LiveRegUnits and handled it locally without needing this helper function in https://github.com/llvm/llvm-project/pull/65962. 

https://github.com/llvm/llvm-project/pull/66061