Remove "Project ID" from Releeph Projects

Summary:
Fixes T3660. Releeph Projects currently have an unused one-to-one mapping to Phabricator projects. This isn't consistent with other applications and has no integrations or uses. Get rid of it.

NOTE: Waiting for signoff from @legneato on T3660 before pulling the trigger here.

Test Plan: Created and edited Releeph projects. Grepped for references to project ID; there are a dozen or so but they're all either Releeph projects or Arcanist projects.

Reviewers: btrahan

Reviewed By: btrahan

CC: LegNeato, aran

Maniphest Tasks: T3660

Differential Revision: https://secure.phabricator.com/D6635