remove helper method page_active?
remove helper method page_active?

this helper was relying on `Page.ancestors_for` which is gone since Alchemy 5.0. We don't need `page_active?` any longer, hence the removal in Alchemy 6.0.

Side note: In a separate commit a hotfix and deprecation notice has been added for Alchemy versions 5.0, 5.1 and 5.2.

robinboening/alchemy_cms,AlchemyCMS/alchemy_cms,AlchemyCMS/alchemy_cms,robinboening/alchemy_cms,AlchemyCMS/alchemy_cms,robinboening/alchemy_cms