4.0.1 release notes: remove a pre-GA leftover

(cherry picked from commit 005bb2c)

Conflicts:
	release-notes/4.1.0.md

Author: michaelklishin

release-notes/4.0.1.md

@@ -218,7 +218,7 @@ Such clusters should be [migrated using the Blue/Green deployment strategy](http
 RabbitMQ 4.0.0 nodes can run alongside `3.13.x` nodes. `4.0.x`-specific features can only be made available when all nodes in the cluster
 upgrade to 4.0.0 or a later patch release in the new series.
 
-While operating in mixed version mode, some aspects of the system may not behave as expected. The list of known behavior changes will be covered in future updates.
+While operating in mixed version mode, some aspects of the system may not behave as expected.
 Once all nodes are upgraded to 4.0.0, these irregularities will go away.
 
 Mixed version clusters are a mechanism that allows rolling upgrade and are not meant to be run for extended