Hide Land to GitHub

Authored by avivey.


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.

Ref T182, T8313

Test Plan: load a diff.

Reviewers: Blessed Reviewers, epriestley

Reviewed By: Blessed Reviewers, epriestley

Subscribers: epriestley

Maniphest Tasks: T182, T8313

Differential Revision: https://secure.phabricator.com/D13022