build: make docs check not required (googleapis#2623)

Author: ddelgrosso1

.github/sync-repo-settings.yaml

@@ -12,7 +12,6 @@ branchProtectionRules:
     requiredStatusCheckContexts:
       - "ci/kokoro: Samples test"
       - "ci/kokoro: System test"
-      - docs
       - lint
       - test (14)
       - test (16)