Remove almost all instances of HeraldContentTypeConfig

Summary: Ref T2769. This cleans up almost every use of the HeraldContentTypeConfig class.

Test Plan: Viewed and edited Herald rules.

Reviewers: btrahan

Reviewed By: btrahan

CC: aran

Maniphest Tasks: T2769

Differential Revision: https://secure.phabricator.com/D6662