Delete Flaky IR Hash Test

Our LLVM backend is supposed to have a build-time optimization where we
hash the IR and do not proceed with LLVM code generation if the hash
matches the one we last used to emit any products. This has never quite
worked for a variety of reasons - we fixed a number of those reasons in
#31106 but this test remained flaky
for its entire lifetime.

It's really not worth all the trouble to keep investigating this, so I'm
removing this test.

rdar://77654695

Author: CodaFi