Hide github registration until backend is implemented

The registration form still displays the option to register and login with github, and I am still in the air on implementing a third auth strategy for what is ultimately a showcase project for my skill set.

Start at the registration form and locate the GitHub registration and login option. Verify the form's current behavior, then confirm the work is done when the GitHub option is no longer displayed while the remaining authentication options still work.

Written by the indexing model from the issue text.