Phriction - sever remaining project ties

Summary: 'cuz the wiki don't play that no more. Fixes T6497. This is mainly important to fix an incorrect policy filtering issue where a project policy can incorrectly override a document policy. Otherwise, it makes things nice and clean.

Test Plan:
- viewed the wiki - success.
- viewed wiki document list under "index" and tried a few different queries
- grep'd for things like "hasProject" and "getProject" and saw no phriction-related results

Reviewers: epriestley

Reviewed By: epriestley

Subscribers: Korvin, epriestley

Maniphest Tasks: T6497

Differential Revision: https://secure.phabricator.com/D10818