Migrate old task transactions to use new display code
Summary: Ref T6027. This converts the old transaction records to the new format so we don't have to keep legacy code around.
Test Plan: Migrated tasks, browsed around, looked at transaction records, didn't see any issues.
Reviewed By: chad
Maniphest Tasks: T6027
Differential Revision: https://secure.phabricator.com/D15637