remove broken gating.yaml

... because the specified gating test does not exist.

gating.yaml

@@ -1,6 +0,0 @@
---- !Policy
-product_versions:
-  - rhel-9
-decision_context: osci_compose_gate
-rules:
-  - !PassingTestCaseRule {test_case_name: osci.brew-build.rpmdeplint.functional}