pw_build: Remove legacy python_wheels
pw_build: Remove legacy python_wheels

The pw_python_wheels target was replaced by a new and improved
version that lives inside pw_build/python_dist now. Known downstream
usages have been updated to use the new version.

No-Docs-Update-Reason: Docs already updated in previous change
Change-Id: I99f70e5f13d0804dd7b1f15274db00b5ca9c484a
Reviewed-on: https://pigweed-review.googlesource.com/c/pigweed/pigweed/+/44145
Reviewed-by: Wyatt Hepler <cca3bedb37979eacd157a9bceb473582df8aea1e@google.com>
Commit-Queue: Joe Ethier <f5eb8cb2f5310c7fa9df6f16eabccb4436f47999@google.com>

google/pigweed,google/pigweed,google/pigweed,google/pigweed,google/pigweed,google/pigweed,google/pigweed,google/pigweed,google/pigweed,google/pigweed