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