Remove command spelling correction from Arcanist

Summary: Fixes T7489. Depends on D16332, which moved this code to libphutil.

Test Plan:

$ arc banch --bystatus
(Assuming 'banch' is the British spelling of 'branch'.)
(Assuming '--bystatus' is the British spelling of '--by-status'.)
...

Reviewers: chad

Reviewed By: chad

Maniphest Tasks: T7489

Differential Revision: https://secure.phabricator.com/D16333