Summary:
Pathway to D17685. This column is a very complicated cache of: is participant.messageCount equal to thread.messageCount?
We can just ask this question with a JOIN instead and simplify things dramatically.
Test Plan:
- Ran migration.
- Browsed around.
- Sent a message, saw unread count go up.
- Read the message, saw unread count go down.
Reviewers: chad
Reviewed By: chad
Differential Revision: https://secure.phabricator.com/D17730
