Successful completion of `#409 </issues/409>`_ (media submission
success messaging) leaves some debris to clean up

these aren't actually used anywhere


-  submit\_success view
-  mediagoblin/submit/success.html template
-  mediagoblin.submit.success route

Chris said,

    Should we have some page that allows us to view all active media
    related to an active tag? Something like: /tag/bunnies/


Why, yes. Yes we should. And by should, I mean, we could, and it
would be very helpful if we did. This feature was rolled over from
`#360 </issues/360>`_.

[BONUS] - /tag/bunnies+fangs

A navigation function in mediagoblin/submit/views.py doesn't seem
to be in use any longer.

::

    def submit_success(request):
        return render_to_response(
            request, 'mediagoblin/submit/success.html', {})

Let's delete it.