Hide Land to GitHub
We don't want to support this right now, so disable it, similar to "Land To Hosted" feature.
Keep to the code as an example for advanced installs.
Test Plan: load a diff.
Reviewers: Blessed Reviewers, epriestley
Reviewed By: Blessed Reviewers, epriestley
Differential Revision: https://secure.phabricator.com/D13022