[llvm] [mlir] [MLIR] [Bazel] Removed the stubgen plumbing added in #179211 (PR #185292)

[Sergei Lebedev via llvm-commits]

superbobry wrote:

The failure in the Bazel build looks unrelated:

```
ERROR: /home/gha/.cache/bazel/_bazel_gha/7e8ec8c8c4975cf00cc8d263f2c10e24/external/+_repo_rules+llvm-project/clang/BUILD.bazel:1851:11: Compiling clang/lib/CodeGen/QualTypeMapper.cpp failed: (Exit 1): clang-22 failed: error executing CppCompile command (from target @@+_repo_rules+llvm-project//clang:codegen) /opt/llvm/bin/clang-22 -U_FORTIFY_SOURCE -fstack-protector -Wall -Wthread-safety -Wself-assign -Wunused-but-set-parameter -Wno-free-nonheap-object -fcolor-diagnostics -fno-omit-frame-pointer '-std=c++17' ... (remaining 349 arguments skipped)

Use --sandbox_debug to see verbose messages from the sandbox and retain the sandbox build root for debugging
In file included from external/+_repo_rules+llvm-project/clang/lib/CodeGen/QualTypeMapper.cpp:17:
external/+_repo_rules+llvm-project/clang/lib/CodeGen/QualTypeMapper.h:24:10: fatal error: 'llvm/ABI/Types.h' file not found
   24 | #include "llvm/ABI/Types.h"
      |   
```

https://github.com/llvm/llvm-project/pull/185292