Add a needle check script, remove some unused needles
    
    I call this...The @lruzicka Catcher!
    
    It's a script that checks for needles that aren't actually used
    anywhere. It also checks for cases where we have a needle JSON
    file but no image, or an image file but no JSON file (and wipes
    one case of the latter). It also adds a run of the script to tox
    so we get it in CI.
    
    You could make this script a lot more elaborate if you like, by
    being fancier about parsing the test code and templates, but I
    don't think it's really warranted, I think it just needs to be
    'good enough'. It's not the end of the world if it misses the
    odd thing or the whitelisting goes stale.
    
    Quite a lot of the removed needles are remnants of different
    approaches to app start/stop testing which weren't caught in the
    initial PR review. The short-name partitioning ones are odd; they
    were introduced in the commit that moved needles into subdirs,
    but at least some of them don't actually appear to be moves. They
    may have been non-tracked files Josef had lying around that got
    into the commit by mistake, or they may just be old needles we
    really used at some point but aren't using any more.
    reclaim_space_second_partition was introduced as part of the
    shrink test (along with reclaim_space_first_partition) but was
    never actually used by that test - I guess, again, the test got
    re-written during review but we forgot to remove the needle. We
    rejigged user creation to use tab presses not a needle match a
    while back, which made user_creation_password_input unnecessary.
    The various cockpit_updates_* needles are I think remnants of
    rewrites of the cockpit update tests that again were missed in
    PR review, the tests as merged never used them.
    
    Signed-off-by: Adam Williamson <awilliam@redhat.com>