Remove deprecated attributes from Milestone

Some fields from Milestone 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/20190221164056_remove_deprecated_translatable_fields_from_milestones.rb

@@ -0,0 +1,6 @@
+class RemoveDeprecatedTranslatableFieldsFromMilestones < ActiveRecord::Migration[4.2]
+  def change
+    remove_column :milestones, :title, :string
+    remove_column :milestones, :description, :text
+  end
+end

db/schema.rb

@@ -985,12 +985,10 @@ ActiveRecord::Schema.define(version: 20190607160900) do
   create_table "milestones", force: :cascade do |t|
     t.string   "milestoneable_type"
     t.integer  "milestoneable_id"
-    t.string   "title",              limit: 80
-    t.text     "description"
     t.datetime "publication_date"
     t.integer  "status_id"
-    t.datetime "created_at",                    null: false
-    t.datetime "updated_at",                    null: false
+    t.datetime "created_at",         null: false
+    t.datetime "updated_at",         null: false
     t.index ["status_id"], name: "index_milestones_on_status_id", using: :btree
   end