Remove unused methods

One method was calling `reason_for_not_being_ballotable_by` passing just
one parameter instead of two.

The other method was calling the method `amount_spent`, which does not
exist in the Budget class.

So both methods would make the application crash if they were called.
Luckily, they aren't, so the application doesn't crash.

app/models/budget.rb

@@ -163,10 +163,6 @@ class Budget < ApplicationRecord
     formatted_amount(heading_price(heading))
   end
 
-  def formatted_heading_amount_spent(heading)
-    formatted_amount(amount_spent(heading))
-  end
-
   def investments_orders
     case phase
     when "accepting", "reviewing"

app/models/budget/investment.rb

@@ -301,10 +301,6 @@ class Budget
       user.headings_voted_within_group(group).where(id: heading.id).exists?
     end
 
-    def ballotable_by?(user)
-      reason_for_not_being_ballotable_by(user).blank?
-    end
-
     def enough_money?(ballot)
       available_money = ballot.amount_available(heading)
       price.to_i <= available_money