chore(pypi): remove unused config settings code

[aignas]

Summary:

• Remove unused pip_* config settings since they have been no op for a while.
• The code was experimental, so it is likely nobody relied heavily on those things.
• Only leave the OSX version flag - we may want to rename that in the future.

Related #260.

[gemini-code-assist]

Code Review

This pull request streamlines the pip integration by removing the enable_pipstar feature, experimental_target_platforms attribute, and legacy configuration flags, while migrating entry point generation to py_console_script_binary. Review feedback highlights dead code regarding the extras parameter in wheel_installer.py and suggests a more robust method for Python version detection in pip_repository.bzl.

[rickeylev]

Remove unused pip_* config settings since they have been no op for a while.

These are unused? I thought the intent was to use them to allow dependency selection when requirement env markers can't do so. e.g., given requirements_musl.txt and requirements_glibc.txt, one would set --pip_lib=musl|glibc to pick between the two closures.