Deprecate "user.enable" and "user.disable" API methods, redefine them in terms of "user.edit"

Summary:
Depends on D19604. Ref T13189. See PHI642. Deprecates these in favor of "user.edit", redefines them in terms of it, and removes the old disableUser() method.

I kept the "is admin" permissions check for consistency, since these methods have always said "(admin only)". This check may not be the most tailored check soon, but we can just keep executing it in addition to the real check.

For now, this change stops this method from actually disabling non-bot users (since it implicitly adds a CAN_EDIT requirement, and even administrators don't have that). An upcoming change will fix that.

Test Plan: Enabled and disabled a (bot) user via these methods. Checked API UI, saw them marked as "disabled".

Reviewers: amckinley

Maniphest Tasks: T13189

Differential Revision: https://secure.phabricator.com/D19605