Switch ACUX client-side events to EventLogging

Replace obsolete client-side trackXx calls with mw.eventLog setDefaults
and logEvent(), reference Schema:AccountCreation, and drop
jquery.clickTracking dependency!  (It still uses CT's ext.UserBuckets.)

Remove the server-side account_create event, it's moved to EventLogging.

Don't log bucket assignment event any more, per Dario.

Change-Id: Ib650de386f9aa20ad31a9418acd48dceb84200b5