Remove optional ClickTracking integration

MoodBar's e-mail notification feature had an optional dependency on
ClickTracking, which it would use to generate links that logged an
analytic event using ClickTracking's API endpoint before redirecting the
user to their original destination. This patch removes this optional
integration but keeps the behavior consistent with how the extension
behaved if ClickTracking was not detected.

This is one of the last few uses of ClickTracking in our deployment
codebase.

Change-Id: I1a22e7d36e24049ca7ccd249df523ef88000e6b2
Merge "Remove optional ClickTracking integration"