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>