Simplify code involving Globalize.locale

We don't need to set this value. In commit f2ef27d3 I made a mistake
thinking `Globalize.locale` and `I18n.locale` should always be in sync,
but they're actually automatically in sync when `Globalize.locale` is
`nil`.

So the best way to avoid any issues is not to assign `Globalize.locale`,
and use `Globalize.with_locale` where necessary instead.

app/controllers/management/base_controller.rb

@@ -46,7 +46,6 @@ class Management::BaseController < ActionController::Base
       session[:locale] ||= I18n.default_locale
 
       I18n.locale = session[:locale]
-      Globalize.locale = I18n.locale
     end
 
     def current_budget