[llvm] CodeGen: Remove target hook for terminal rule (PR #165962)

[via llvm-commits]

appujee wrote:

Can we add a target specific hook to disable `applyTerminalRule` e.g., enable this only when `shouldRewriteCopySrc` returns true? We are seeing a failure on a copy instruction of a non-general purpose register and I wonder how we can get around this optimization.

https://github.com/llvm/llvm-project/pull/165962