[llvm] [AMDGPU] Remove SIProgramInfo related MCExpr unittest (PR #91758)

[Janek van Oirschot via llvm-commits]

JanekvO wrote:

> We already have the build fix, why drop test coverage

When I was adding this unittest at the time I was already feeling a bit conflicted about this unittest, so I may be biased.

I believe that eventually this unittest will either have to be changed/removed regardless. The unittest currently serves the purpose of testing the conversion of MCExprs back to known values through the MCExpr's `evaluateAsAbsolute` call. This is a scenario that will never fail under current circumstances as the MCExprs originate and are constructed from known values (which is why I cannot reproduce through regression tests and need to force it through using a unittest). I'm working on changing the consumers of `SIProgramInfo` to directly support MCExprs which would remove the aforementioned conversion from MCExpr to known values.

Again, if the desire to keep this unittest in then that's fine as well and we can move forward with #91727.

https://github.com/llvm/llvm-project/pull/91758