Remove deprecated attributes from Poll

Some fields from Poll are translatable and we no longer need them. This
commit will remove the annoying deprecation warning thrown by Globalize
gem after gem version update.

db/migrate/20190221162450_remove_deprecated_translatable_fields_from_polls.rb

@@ -0,0 +1,7 @@
+class RemoveDeprecatedTranslatableFieldsFromPolls < ActiveRecord::Migration[4.2]
+  def change
+    remove_column :polls, :name, :string
+    remove_column :polls, :summary, :text
+    remove_column :polls, :description, :text
+  end
+end

db/schema.rb

@@ -1256,13 +1256,10 @@ ActiveRecord::Schema.define(version: 20190607160900) do
   end
 
   create_table "polls", force: :cascade do |t|
-    t.string   "name"
     t.datetime "starts_at"
     t.datetime "ends_at"
     t.boolean  "published",          default: false
     t.boolean  "geozone_restricted", default: false
-    t.text     "summary"
-    t.text     "description"
     t.integer  "comments_count",     default: 0
     t.integer  "author_id"
     t.datetime "hidden_at"