Remove loadReleephBranch and loadReleephProject from ReleephRequest

Summary: Ref T3551. Ref T3549. Mostly unnecessary with modern calls.

Test Plan:

• Called releeph.queryrequests.
• Called releeph.request.
• Called releephwork.getbranchcommitmessage.
• Called releephwork.getcommitmessage.
• Called releephwork.nextrequest.
• Viewed and edited branches and requests.
• Made a comment on a request.

Reviewers: btrahan

Reviewed By: btrahan

Subscribers: epriestley

Maniphest Tasks: T3549, T3551

Differential Revision: https://secure.phabricator.com/D8820