[5.1.x] Removed advice to propose a new contrib app.

Backport of 9d22a7d from main.

Author: sarahboyce

docs/ref/contrib/index.txt

@@ -133,9 +133,3 @@ See the :doc:`sitemaps documentation </ref/contrib/sitemaps>`.
 A framework for generating syndication feeds, in RSS and Atom, quite easily.
 
 See the :doc:`syndication documentation </ref/contrib/syndication>`.
-
-Other add-ons
-=============
-
-If you have an idea for functionality to include in ``contrib``, let us know!
-Code it up, and post it to the |django-users| mailing list.