Add a "remove projects" action to Herald

Summary: Fixes T7849. This adds "Remove Projects" to all objects which implement PhabricatorProjectInterface.

Test Plan:

• Wrote a rule to remove a project, edited task, saw the project removed.
• Admired entirely reasonable implementation complexity.

Reviewers: btrahan

Reviewed By: btrahan

Subscribers: epriestley

Maniphest Tasks: T7849

Differential Revision: https://secure.phabricator.com/D12505