Remove RTD integration now that it isn't requiremed (#684)

Author: ericholscher

docs/contributing.rst

@@ -87,7 +87,3 @@ you should do the following:
         $ rm -rf dist/
         $ python setup.py sdist bdist_wheel
         $ twine upload --sign --identity [email protected] dist/*
-
-#. In the ``readthedocs.org`` repo, edit the ``bower.json`` file to point at the correct version
-   (``sphinx-rtd-theme": "https://github.com/rtfd/sphinx-rtd-theme.git#$NEW_VERSION"``).
-#. In the ``readthedocs.org`` repo, run ``gulp build`` to update the distributed theme files.