Address review comment.

Clearer "this is deprecated" wording.

Co-authored-by: Tennessee Carmel-Veilleux <tennessee.carmelveilleux@gmail.com>

Author: bzbarsky-apple

src/app/CASEClient.h

@@ -35,9 +35,10 @@ struct CASEClientInitParams
     FabricTable * fabricTable                                          = nullptr;
     Credentials::GroupDataProvider * groupDataProvider                 = nullptr;
 
-    // mrpLocalConfig should not generally be set to anything other than
+    // `mrpLocalConfig` should not generally be set to anything other than
     // NullOptional.  Doing that can lead to different parts of the system
-    // claiming different MRP parameters for the same node.
+    // claiming different MRP parameters for the same node. This remains
+    // as backwards compatibility to previous public API.
     Optional<ReliableMessageProtocolConfig> mrpLocalConfig = NullOptional;
 
     CHIP_ERROR Validate() const