R1:0036670329cc

Remove remaining arcanist project code

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…