[llvm] [bazel] Revert "[bazel] llvm-config.h: Turn on LLVM_ENABLE_PLUGINS" as it fails TensorFlow Windows build (PR #143419)

[Reid Kleckner via llvm-commits]

https://github.com/rnk approved this pull request.

Let's roll it back. I've been struggling to replicate this failure locally to attempt to debug further, but let's go ahead and land this in the meantime.

https://github.com/llvm/llvm-project/pull/143419