Don't open symbols on double click

Summary:
My average double click speed is 10 ms but I tried to double click as I think normal people double clicks and it was around 200 ms.
I don't want to make the timeout much longer because it looks like that something doesn't work.

Test Plan:
Double clicked on symbol.
Clicked on symbol.

Reviewers: epriestley

Reviewed By: epriestley

CC: aran, Korvin

Differential Revision: https://secure.phabricator.com/D3509