remove STI test
    
    The test fails because of the same reason as the installability test,
    it tries to install every subpackage which fails because the standalone
    subpackages conflict with all the other packages.
    
    Given there's no owner for the test, nobody looks at or seems interested
    in the results, STI itself will likely be deprecated soon
    (https://fedoraproject.org/wiki/Changes/DeprecateSTI) and systemd's
    upstream integration tests will soon support checking for AVC denials
    (https://github.com/systemd/systemd/pull/35921), let's remove the STI test.