Remove several "loadArcanistProject()" methods

Summary:
Ref T3551. Releeph has old-style loadX() methods; get rid of one of them.

Differential has a couple of copies of this too, clean them up.

Test Plan:

• Viewed various differential revisions (with and without projects).
• Viewed and edited Releeph products.

Reviewers: btrahan

Reviewed By: btrahan

Subscribers: epriestley

Maniphest Tasks: T3551

Differential Revision: https://secure.phabricator.com/D8768