[llvm] Revert "[bazel][mlir][python] Port #155741: stub auto-generation (#157173)" (PR #157995)

[Alex Trotta via llvm-commits]

Ahajha wrote:

We run mypy on our python files, and removing the stubfiles does break things. I would prefer to just revert to how it was before since we'll have to integrate the stub generation into our build at a later point once it's relanded, and this avoids a temporary workaround.

https://github.com/llvm/llvm-project/pull/157995