ci: remove circleci required status from angular robot

The build job moved from CircleCI to GitHub actions, so we currently
mark all PRs as pending unnnecessarily.

In the future, this will be replaced by the unified status check. It's
set up here but was disabled at some point. Needs more investigation.

.github/angular-robot.yml

@@ -68,7 +68,6 @@ merge:
 
     # list of PR statuses that need to be successful
     requiredStatuses:
-      - 'ci/circleci: build'
       - 'google-internal-tests'
       - 'pullapprove'