[llvm] Revert "[GlobalISel] Add support for lowering byref attribute" (PR #96784)

[Thorsten Schütt via llvm-commits]

tschuett wrote:

Now, I am even less convinced of the original PR. It had no tests, which is almost forbidden. There was an explicit request for tests. 

Now, you are saying that `byref` is rarely used.

Dead code with no tests? I still vote for revert.

https://github.com/llvm/llvm-project/pull/96784