Revert "slack-config/sig-release: Add #release-team-leads channel (#6324)"

This reverts commit 19a4ae7.

Slack channels and names share a namespace and cannot be called the same thing.

Author: mrbobbytables

communication/slack-config/sig-release/config.yaml

@@ -8,4 +8,3 @@ channels:
   - name: release-management
     id: CJH2GBF7Y
   - name: release-notes
-  - name: release-team-leads