[NFC] [C++20] [Modules] Remove pr60085.cppm with deprecated practice

See https://github.com/llvm/llvm-project/issues/60085 for the complete
story.

Previously I thought the problem got fixed surprisingly. But it is not
true. I just tested it with a deprecated method. My bad. Then the
deprecated style should be removed and the proper style can't work. So
I'll remove the test and reopen that issue to look into it.