doc: release-notes-4.1: Mention removal of deprecated HCI API

Mention the removed deprecated Bluetooth HCI driver API.

Signed-off-by: Johan Hedberg <[email protected]>

Author: jhedberg

doc/releases/release-notes-4.1.rst

@@ -27,6 +27,9 @@ API Changes
 Removed APIs in this release
 ============================
 
+ * The deprecated Bluetooth HCI driver API has been removed. It has been replaced by a
+   :c:group:`new API<bt_hci_api>` that follows the normal Zephyr driver model.
+
 Deprecated in this release
 ==========================