Move relation includes out of query object

This query object is meant to be reusable but those includes are
context-specific and will likely not be needed when reusing the query
elsewhere. If we keep them there, chances are next dev might not notice
it and will introduce a performance regression.

app/controllers/admin/customers_controller.rb

@@ -65,7 +65,8 @@ module Admin
 
     def collection
       if json_request? && params[:enterprise_id].present?
-        CustomersWithBalance.new(managed_enterprise_id).query
+        CustomersWithBalance.new(managed_enterprise_id).query.
+          includes(:bill_address, :ship_address, user: :credit_cards)
       else
         Customer.where('1=0')
       end

app/services/customers_with_balance.rb

@@ -7,7 +7,6 @@ class CustomersWithBalance
 
   def query
     Customer.of(enterprise_id).
-      includes(:bill_address, :ship_address, user: :credit_cards).
       joins(left_join_non_cart_orders).
       group("customers.id").
       select("customers.*").