Remove temp testing workflow & route on-demand workflow to selfhosted runner (#1282)

Author: rzats

.github/workflows/performance-tests-periodic.yml

@@ -14,7 +14,8 @@ jobs:
   run-perftests:
     # Make sure 1. this is a PR, not an issue 2. it contains "/run performance test" anywhere in the body
     if: github.event.issue.pull_request && contains(github.event.comment.body, '/run performance test')
-    runs-on: ubuntu-latest
+    # Run this on Delphi's self-hosted runner
+    runs-on: self-hosted
     outputs:
       request_count: ${{ steps.output.outputs.request_count }}
       failure_count: ${{ steps.output.outputs.failure_count }}