[llvm] [AMDGPU] Remove target feature `DumpCode` and `DumpCodeLower` (PR #176960)

[Matt Arsenault via llvm-commits]

arsenm wrote:

> A proactive follow-up of #176844. Feel free to close it if this feature is still used downstream.

Or, we rip it out and force downstream action. This is long, long overdue 

https://github.com/llvm/llvm-project/pull/176960