ci: removing clirr from required checks (#421)

Making CLIRR not required. The version bumps are now controlled by the Release Please and OwlBot. The CL authors create appropriate change description to control major version bumps.

Author: suztomo

.github/sync-repo-settings.yaml

@@ -11,7 +11,6 @@ branchProtectionRules:
       - dependencies (8)
       - dependencies (11)
       - lint
-      - clirr
       - units (8)
       - units (11)
       - 'Kokoro - Test: Integration'
@@ -26,7 +25,6 @@ branchProtectionRules:
       - dependencies (8)
       - dependencies (11)
       - lint
-      - clirr
       - units (7)
       - units (8)
       - units (11)