chore: remove unused which.bzl helper

[rickeylev]

Nothing loads which.bzl, so remove it.

[gemini-code-assist]

Summary of Changes

Hello @rickeylev, I'm Gemini Code Assist¹! I'm currently reviewing this pull request and will post my feedback shortly. In the meantime, here's a summary to help you and other reviewers quickly get up to speed!

This pull request focuses on code maintenance by removing an identified unused helper file. The which.bzl file, containing a utility function, has been entirely deleted, contributing to a leaner and more maintainable project structure.

Highlights

• Code Cleanup: Removed the python/private/which.bzl file, which contained an unused which_with_fail helper function. This file was not loaded by any other part of the codebase.

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[gemini-code-assist]

Code Review

This pull request correctly removes the python/private/which.bzl file. After reviewing the provided code context, it's clear that the functionality previously contained within which.bzl has been superseded or reimplemented in python/private/repo_utils.bzl, making which.bzl an unused helper file. The removal simplifies the codebase without impacting existing functionality.