samples: nrf5340: changelog for multiprotocol_rpmsg removal

The samples/nrf5340/multiprotocol_rpmsg is removed.
Add changelog entry.

Signed-off-by: Andrzej Kuros <[email protected]>

Author: ankuns

doc/nrf/releases_and_maturity/releases/release-notes-changelog.rst

@@ -336,7 +336,8 @@ NFC samples
 nRF5340 samples
 ---------------
 
-|no_changes_yet_note|
+* Removed the ``nRF5340: Multiprotocol RPMsg`` sample.
+  Use the :ref:`ipc_radio` application instead.
 
 Peripheral samples
 ------------------