[llvm] Revert [clang] Handle templated operators with reversed arguments and [STLExtras] Undo C++20 hack (PR #69937)

[via llvm-commits]

dyung wrote:

This revert seems to have broken quite a few build bots with the test failure @nico mentioned. Can you please look into this so we can get the bots green again?
- https://lab.llvm.org/buildbot/#/builders/164/builds/45362
- https://lab.llvm.org/buildbot/#/builders/188/builds/36986
- https://lab.llvm.org/buildbot/#/builders/197/builds/10402
- https://lab.llvm.org/buildbot/#/builders/245/builds/15680
- https://lab.llvm.org/buildbot/#/builders/258/builds/8447
- https://lab.llvm.org/buildbot/#/builders/121/builds/35809
- https://lab.llvm.org/buildbot/#/builders/230/builds/20289
- https://lab.llvm.org/buildbot/#/builders/91/builds/20979
- https://lab.llvm.org/buildbot/#/builders/109/builds/76025
- https://lab.llvm.org/buildbot/#/builders/36/builds/39047
- https://lab.llvm.org/buildbot/#/builders/54/builds/6960
- https://lab.llvm.org/buildbot/#/builders/275/builds/38
- https://lab.llvm.org/buildbot/#/builders/139/builds/52005
- https://lab.llvm.org/buildbot/#/builders/216/builds/29174

https://github.com/llvm/llvm-project/pull/69937