[llvm] Revert "Reland [EquivClasses] Introduce members iterator-helper" (PR #130380)

[LLVM Continuous Integration via llvm-commits]

llvm-ci wrote:

LLVM Buildbot has detected a new failure on builder `arc-builder` running on `arc-worker` while building `llvm` at step 6 "test-build-unified-tree-check-all".

Full details are available at: https://lab.llvm.org/buildbot/#/builders/3/builds/12787

<details>
<summary>Here is the relevant piece of the build log for the reference</summary>

```
Step 6 (test-build-unified-tree-check-all) failure: 1200 seconds without output running [b'ninja', b'check-all'], attempting to kill
...
9.410 [84/18/20] cd /buildbot/worker/arc-folder/llvm-project/clang/bindings/python && /usr/local/bin/cmake -E env CLANG_NO_DEFAULT_CONFIG=1 CLANG_LIBRARY_PATH=/buildbot/worker/arc-folder/build/lib /usr/local/bin/python3.9 -m unittest discover
..........................................................................................................................................................
----------------------------------------------------------------------
Ran 154 tests in 1.407s

OK
9.450 [83/18/21] Linking CXX executable tools/clang/unittests/Driver/ClangDriverTests
10.506 [82/18/22] Linking CXX executable tools/clang/unittests/Analysis/FlowSensitive/ClangAnalysisFlowSensitiveTests
12.071 [81/18/23] Building CXX object unittests/ADT/CMakeFiles/ADTTests.dir/EquivalenceClassesTest.cpp.o
13.835 [80/18/24] Linking CXX executable unittests/ADT/ADTTests
command timed out: 1200 seconds without output running [b'ninja', b'check-all'], attempting to kill
process killed by signal 9
program finished with exit code -1
elapsedTime=1281.590132

```

</details>

https://github.com/llvm/llvm-project/pull/130380