bug 1042820 - moor tidy of apps/amo

Not all of it, by a long way, but the bits I could clearly see were used or unused.  Also I figured I better push the progress so far while its still (semi-) understandable.
I'd prefer to move this to `mkt/developers/fields.py` (which doesn't exist yet). Also, fix the import issue (`fields` is not imported)