Fix "Resolve conflicts in user activity"

db/migrate/20161007073613_create_user_activities.rb

@@ -25,4 +25,3 @@ class CreateUserActivities < ActiveRecord::Migration
     end
   end
 end
-

db/post_migrate/20161128170531_drop_user_activities_table.rb

@@ -32,4 +32,3 @@ class DropUserActivitiesTable < ActiveRecord::Migration
     end
   end
 end
-