Remove scap-security-guide from tiers
    
    We already run daily testing of to-be-released scap-security-guide
    against latest RHEL nightlies, and we maintain a list of known
    failures compared to that version.
    
    Running tests against the released version of scap-security-guide
    here in tiers not only wastes computing resources (any issues found
    we wouldn't fix until the next release, tested by our daily runs),
    but it also requires us to maintain a copy of the list of known
    failures, specifically for this "old" released scap-security-guide.
    
    Therefore, we came to the conclusion that we don't want to run
    scap-security-guide (content) tests here in tiers.