Delete old Maniphest edit controller
Ref T9908. No more callsites. Also:
- Phurl a couple of documentation URIs.
- Get rid of "task:" in the global search since it doesn't really make sense anymore.
Test Plan: grep, edited/created tasks.
Reviewed By: chad
Maniphest Tasks: T9908
Differential Revision: https://secure.phabricator.com/D14716