Remove dirinstall functional test.

The test was not migrated from dist-git branch when c8s was created.
It should be either migrated to tmt/fmf solution as in c9s or removed.
We decided to remove it as its value compared to rtt which stay in place
is negligible.

gating.yaml

@@ -3,5 +3,4 @@ product_versions:
   - rhel-8
 decision_context: osci_compose_gate
 rules:
-  - !PassingTestCaseRule {test_case_name: osci.brew-build.tier0.functional}
   - !PassingTestCaseRule {test_case_name: rtt.gating.functional}