Avoid 'new' to create a deferred

As per http://api.jquery.com/jQuery.Deferred/ the new operator is optional.
So remove the new operator to make $.Deferred usage consistent with
other parts of source code.

Also see https://gerrit.wikimedia.org/r/174330

Change-Id: Ib5dbe0d2943cd19a842e03ae5d9e942f02eeccfb
Merge "Avoid 'new' to create a deferred"