Remove unused heading

docs/releases/6.4.md

@@ -244,8 +244,6 @@ def test_search(self):
     self.assertContains(response, "Christmas party")
 ```
 
-## Upgrade considerations - deprecation of old functionality
-
 ## Upgrade considerations - changes affecting Wagtail customizations
 
 ### Added `page` as a third parameter to the `construct_wagtail_userbar` hook