Summary: Fixes T7604. This is the big scary change which drops the "arcanist project" fields from the database permanently.
Test Plan:
`grep`ped for the following to ensure that I had found all remaining references:
- `/arcanistProject/i`
- `/arcanist_project/i`
- `/projectName/i`
- `/project_name/i`
- `/project_id/i`
WARNING: Wait at least one month before landing this.
Reviewers: epriestley, #blessed_reviewers
Reviewed By: epriestley, #blessed_reviewers
Subscribers: Korvin, epriestley
Maniphest Tasks: T7604
Differential Revision: https://secure.phabricator.com/D12899
