Revert "[clang] - Add missing builtin name to AtomicExpr JSON dump"

This reverts commit dbccf3c6.

The test added is failing on many bots including:
- https://lab.llvm.org/buildbot/#/builders/164/builds/42716
- https://lab.llvm.org/buildbot/#/builders/188/builds/34429
- https://lab.llvm.org/buildbot/#/builders/245/builds/13103
- https://lab.llvm.org/buildbot/#/builders/258/builds/6002
- https://lab.llvm.org/buildbot/#/builders/230/builds/17690
- https://lab.llvm.org/buildbot/#/builders/91/builds/17722
- https://lab.llvm.org/buildbot/#/builders/67/builds/12466
- https://lab.llvm.org/buildbot/#/builders/109/builds/72108
- https://lab.llvm.org/buildbot/#/builders/139/builds/48265
- https://lab.llvm.org/buildbot/#/builders/216/builds/26208
- https://lab.llvm.org/buildbot/#/builders/36/builds/36964
- https://lab.llvm.org/buildbot/#/builders/247/builds/8222