remove leftover admonition

Author: rustagir

source/whats-new.txt

@@ -34,17 +34,6 @@ Learn what's new by version:
 What's New in 1.11
 --------------------
 
-.. important:: Breaking Changes in Tombstone Event Creation
-   
-   This release adds the ``change.stream.document.key.as.key`` source
-   connector configuration property and sets it to ``true`` by default.
-
-   Now, tombstone events use the keys of deleted documents as source record
-   keys. To revert the tombstone event behavior, set
-   ``change.stream.document.key.as.key`` to ``false``. To learn more
-   about this property, see the list of :ref:`Change Stream Properties
-   <source-configuration-change-stream-list>`.
-
 - Added support for regular expressions in the ``topic.namespace.map`` property.
 
 - Added support for setting a custom delete write model strategy by using the