Remove Community labels from Contractor MRs

What does this MR do and why?

As a follow on from !2760 (merged)

This updates the automation to remove Community contribution and Leading Organization labels from non-community Contractor Contribution MRs

Expected impact & dry-runs

https://gitlab.com/gitlab-org/quality/triage-ops/-/jobs/6625821018

No 'new' MRs turned up during dry run, this will only affect 'new' instances. I'll investigate the need for a separate one-off policy if necessary.

Action items

• If adding environment variables for reactive processors, update config/triage-web.yaml and .gitlab/ci/triage-web.yml
• (If applicable) Add documentation to the handbook pages for Triage Operations =>
• (If applicable) Identify the affected groups and how to communicate to them:
  • /cc @person_or_group =>
  • Relevant Slack channels =>
  • Engineering week-in-review