Removed most of the deprecated shoppingcart app, leaving just enough to allow us to cleanly remove the related database tables later. Also removed the relevant Django settings that weren't in use elsewhere.
This is a transitional folder as we move away from modifying ``sys.path`` in django config. See `the ADR`_ for more details. .. _the ADR: https://github.com/edx/edx-platform/blob/master/docs/decisions/0007-sys-path-modification-removal.rst