Diffusion - nuke faulty javascript error handler
Summary: Fixes T3913.
Test Plan: messed around with a comment on a commit and saw preview still updating correctly
Reviewers: epriestley
Reviewed By: epriestley
Subscribers: epriestley, Korvin
Maniphest Tasks: T3913
Differential Revision: https://secure.phabricator.com/D10382