Tests for ConferenceRegistrations controller

Authorization needs to be done first or else it will give
CanCan::AuthorizationNotPerformed error for some of branches.
Removed if condition is dead code.
Small fix in flash message of destroy and its feature test.

spec/factories/registration.rb

@@ -4,5 +4,6 @@ FactoryGirl.define do
   factory :registration do
     user
     conference
+    arrival 3.days.ago
   end
 end