Summary: Deleted the channel field and added a sql patch to drop the channel field.
Test Plan: I have messed up my local mysql:P, hence by storage upgrade is failing. Anyways, The chatlog_event table shouldn't contain the channel column now.
Reviewers: epriestley
Reviewed By: epriestley
CC: aran, Korvin
Differential Revision: https://secure.phabricator.com/D5011
