drop our implementation of script_run in favour of os-autoinst
    
    Summary:
    os-autoinst implements `script_run` itself now, we aren't
    required to implement it ourselves any more. os-autoinst's
    implementation is better than ours, as it allows for verifying
    the script actually ran (via the redirect-output-to-serial-
    console trick).
    
    So this drops our implementation so we'll just use the upstream
    one. Where I judged we don't want to bother with the 'check
    the command actually ran' feature I've adjusted our direct
    `script_run` calls to pass a wait time of 0, which skips the
    'wait for command to run' stuff entirely and just does a simple
    'type the string and hit enter'.
    
    Because of how the inheritance works, our `assert_script_run`
    calls already used the os-autoinst `script_run`, rather than
    the one from our distribution.
    
    This should prevent `prepare_test_packages` sometimes going
    wrong right after removing the python3-kickstart package, as
    we'll properly wait for that removal to complete now (before
    we weren't, we'd just start typing the next command while it
    was still running, which could result in lost keypresses).
    
    Test Plan:
    Check all tests still run OK (I've tried this on
    staging and it seems fine).
    
    Reviewers: jskladan, garretraziel
    
    Reviewed By: garretraziel
    
    Subscribers: tflink
    
    Differential Revision: https://phab.qadevel.cloud.fedoraproject.org/D1034