Simplify scope usage

Rails automatically calls the `id` method inside scopes and the variable
name makes more sense if it represents investments instead of the number
of investments.

app/controllers/valuation/budgets_controller.rb

@@ -7,10 +7,9 @@ class Valuation::BudgetsController < Valuation::BaseController
   def index
     @budget = current_budget
     if @budget.present?
-      @investments_with_valuation_open = @budget.investments
-                                                .by_valuator(current_user.valuator.try(:id))
-                                                .valuation_open
-                                                .count
+      @investments = @budget.investments
+                            .by_valuator(current_user.valuator)
+                            .valuation_open
     end
   end
 end

app/views/valuation/budgets/index.html.erb

@@ -18,7 +18,7 @@
         <%= t("budgets.phase.#{@budget.phase}") %>
       </td>
       <td>
-        <%= @investments_with_valuation_open %>
+        <%= @investments.count %>
       </td>
       <td>
         <%= link_to t("valuation.budgets.index.evaluate"),