R1:8bca296ac141

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.

Reviewers: chad

Reviewed By: chad

Maniphest Tasks: T6027

Differential Revision: https://secure.phabricator.com/D15637