removes heading reference in ballot

heading info is stored per group in ballot_lines

db/schema.rb

@@ -11,7 +11,7 @@
 #
 # It's strongly recommended that you check this file into your version control system.
 
-ActiveRecord::Schema.define(version: 20160610094658) do
+ActiveRecord::Schema.define(version: 20160614091639) do
 
   # These are extensions that must be enabled in order to support this database
   enable_extension "plpgsql"
@@ -96,11 +96,8 @@ ActiveRecord::Schema.define(version: 20160610094658) do
     t.integer  "budget_id"
     t.datetime "created_at", null: false
     t.datetime "updated_at", null: false
-    t.integer  "heading_id"
   end
 
-  add_index "budget_ballots", ["heading_id"], name: "index_budget_ballots_on_heading_id", using: :btree
-
   create_table "budget_groups", force: :cascade do |t|
     t.integer "budget_id"
     t.string  "name",      limit: 50