R1:9141da84c85c

Maniphest - convert old CC transactions to modern SUBSCRIBER transactions

Summary: database migration + drop old view code. Fixes T5604.

Test Plan: grepped src/ for TYPE_CCS (no hits); viewed some tasks with old cc transactions and noted they still rendered correctly post data conversion

Reviewers: epriestley

Reviewed By: epriestley

Subscribers: Korvin, epriestley

Maniphest Tasks: T5604

Differential Revision: https://secure.phabricator.com/D11015