chore(python): remove configure_previous_major_version_branches#288

Linchin merged 3 commits intomaingoogleapis/python-test-utils:mainfrom

owl-bot-update-lock-fbbc8db67afd8b7d71bf694c5081a32da0c528eba166fbcffb3b6e56ddf907d5googleapis/python-test-utils:owl-bot-update-lock-fbbc8db67afd8b7d71bf694c5081a32da0c528eba166fbcffb3b6e56ddf907d5Copy head branch name to clipboard