Unprototype "Facts" to clear Maniphest/chart fatals

Summary: Ref T13279. Facts is still fairly rough, but not broken/policy-violating, so it can be unprototyped to fix the issue where Maniphest reports (which are now driven by Facts) don't work if prototypes are disabled.

Test Plan: Viewed Maniphest reports and Project reports with prototypes on/off and Fact installed/uninstalled.

Subscribers: yelirekim

Maniphest Tasks: T13279

Differential Revision: https://secure.phabricator.com/D20822