[llvm] [coro][pgo] Remove redundant coroutine test files (PR #89620)

[via llvm-commits]

zmodem wrote:

> This was intentional, see the comment that introduced them ([#71262 (review)](https://github.com/llvm/llvm-project/pull/71262#pullrequestreview-1723261241))

I saw that, but I don't agree with the outcome :-)

> An advantage is that the tests cover 2 concerns, really: coro lowering, and PGO instrumentation. They can potentially diverge if needed.

The original tests (e.g. llvm/test/Transforms/Coroutines/coro-split-musttail.ll) already cover both concerns nicely.

If there's a need to diverge, new tests could be created when that need arises.

> Other than needing to duplicate a fix in both places, is there any other shortcoming of the double presence?

Needing to update two almost identical copies of 12 tests is a pretty big pain.

https://github.com/llvm/llvm-project/pull/89620