Successful completion of #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.

[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.