Don't return the created EventSearch.

Reasons:

1. Actually, this is a hack.  There's a glitch in current Ember Data
   where embedded entities returned from the server are re-read and
   prepared to be reinserted into a Store, but one of two undesirable
   behaviors happen:

   a. If the embedded entity has an "id" property and an entity with the
      same ID already exists in a Store, an error will be raised.
   b. If the embedded entity has a primary key that is not "id" (but is
      nevertheless declared via the Adapter), the embedded entity will
      be inserted into the target Store.  This will almost always create
      a duplicate record.

2. Despite the hackish nature of (1), returning the created EventSearch
   isn't necessary because the client determines the entire content of
   an EventSearch object.  (Well, almost.  The ID isn't calculated
   client-side, but that isn't that important -- and if I want more
   purity I can just calculate a UUID client-side.)  All the client
   needs is acknowledgment.