Let Globalize use I18n locale

This is a mistake I made in commit f2ef27d3. Back then I thought we
needed to keep Globalize.locale and I18n.locale in sync, but the truth
is it automatically happens when setting Globalize.locale to nil.

So now we can use I18n.with_locale (at least in the tests) and forget
about Globalize, which will make it easier to switch to Mobility in the
future.

spec/features/admin/budget_investments_spec.rb

@@ -824,9 +824,7 @@ describe "Admin budget investments" do
 
     before do
       I18n.with_locale(:es) do
-        Globalize.with_locale(:es) do
-          create(:budget_investment, title: "Proyecto de inversión", budget: budget)
-        end
+        create(:budget_investment, title: "Proyecto de inversión", budget: budget)
       end
     end