R1:a1499ceb8f61

Don't let autoplans be run manually

Summary: Ref T8096. Like stop/start, autoplans are pushed into the system from outside (normally by `arc`) so it doesn't make any sense to run them manually.

Test Plan:
- Tried to run an autoplan from web UI, got an error.
- Ran a normal plan from web UI.
- Tried to run an autoplan from CLI, got an error.
- Ran a noraml plan from CLI.

Reviewers: chad

Reviewed By: chad

Maniphest Tasks: T8096

Differential Revision: https://secure.phabricator.com/D13844