Clean up minimal browser environment setup
    
    Move the xauth disablement and the disabling of studies into
    _setup_browser, instead of repeating it in a couple of other
    places (but *not* doing it in the zezere test, where we should
    be doing it). Drop some explicit package installs that should
    no longer be needed as Firefox and/or X.org now depend on those
    things. Install the current default fonts (Noto), not the old
    ones (DejaVu).
    
    Signed-off-by: Adam Williamson <awilliam@redhat.com>