Remove pointless requireCapabilities() method from PhabricatorProjectColumnTransactionEditor

Summary:
Depends on D19581. Ref T13164. This method has no effect:

• You must always have CAN_EDIT to reach an Editor in the first place.
• Per previous change, I'm going to restructure this so transactions explicitly check CAN_EDIT by default anyway.

Test Plan: Tried to edit and hide a project column as a user without permission, hit global permission checks long before reaching this method.

Reviewers: amckinley

Reviewed By: amckinley

Maniphest Tasks: T13164

Differential Revision: https://secure.phabricator.com/D19582