portfolio/pages: Correct collection deletion info

There was an old reference to collection deletion left
that alluded to the old information. From 21.04 on it
is possible to delete a collection in one go.

source/portfolio/pages.rst

@@ -184,7 +184,7 @@ You can find additional options for pages or collections via the *More options*
 #. Click *Delete* |delete icon| to :ref:`delete the page <delete_page>` or delete the collection.
 
    .. note::
-      If you delete a collection, the pages and artefacts within it are not deleted.
+      If you delete a collection, the pages and artefacts within it will be deleted.
 
 #. **Created**: The date and time when you set up the page or collection.
 #. **Modified**: The last time you made a change to the page or collection.