Remove "arcanist projects" from Releeph

Summary: Ref T7604. Remove arcanist projects from Releeph.

Test Plan: I don't really know how to use Releeph but I clicked around and nothing seemed too broken.

Reviewers: Blessed Reviewers, epriestley

Reviewed By: Blessed Reviewers, epriestley

Subscribers: Korvin, epriestley

Maniphest Tasks: T7604

Differential Revision: https://secure.phabricator.com/D12898