Fix tabs losing scroll position

Summary: we were missing an e.kill(). Fixes T5754.

Test Plan: looked at a file and selected different tabs - pre-patch vertical position lost and post patch vertical position preserved!

Reviewers: chad, epriestley

Reviewed By: epriestley

Subscribers: epriestley, Korvin

Maniphest Tasks: T5754

Differential Revision: https://secure.phabricator.com/D10111