chore: revert owlbot main branch templates (#171)

Author: dandhlee

owlbot.py

@@ -44,43 +44,3 @@
 
 s.shell.run(["nox", "-s", "blacken"], hide_output=False)
 
-# ----------------------------------------------------------------------------
-# Main Branch migration
-# ----------------------------------------------------------------------------
-
-s.replace(
-  "*.rst",
-  "master",
-  "main"
-)
-
-s.replace(
-  "README.rst",
-  "google-cloud-python/blob/main/README.rst",
-  "google-cloud-python/blob/master/README.rst"
-)
-
-s.replace(
-  "CONTRIBUTING.rst",
-  "kubernetes/community/blob/main",
-  "kubernetes/community/blob/master"
-)
-
-s.replace(
-  "docs/conf.py",
-  "master",
-  "main"
-)
-
-s.replace(
-  "docs/conf.py",
-  "main_doc",
-  "root_doc"
-)
-
-s.replace(
-  ".kokoro/*",
-  "master",
-  "main"
-)
-