/dmails: don't default to 'received' folder.

Don't make /dmails default to the received folder when no other folder
is specified. This is surprising in the API because it means
/dmails.json only shows received dmails by default, not all dmails. This
isn't necessary either since everything that links to dmails already
specifies the received folder.

app/controllers/dmails_controller.rb

@@ -15,7 +15,7 @@ class DmailsController < ApplicationController
   end
 
   def index
-    @dmails = Dmail.visible.paginated_search(params, defaults: { folder: "received" }, count_pages: true)
+    @dmails = Dmail.visible.paginated_search(params, count_pages: true)
     @dmails = @dmails.includes(:owner, :to, :from) if request.format.html?
 
     respond_with(@dmails)