GCS_MAVLink: add timeline for removal of MISSION_REQUEST handling

Author: peterbarker

libraries/GCS_MAVLink/GCS_config.h

@@ -87,8 +87,13 @@
 
 // GCS should be using MISSION_REQUEST_INT instead; this is a waste of
 // flash.  MISSION_REQUEST was deprecated in June 2020.  We started
-// sending warnings to the GCS in Sep 2022 if this command was used.
+// sending warnings to the GCS in Sep 2022 if MISSION_REQUEST was used.
 // Copter 4.4.0 sends this warning.
+// CODE_REMOVAL
+// ArduPilot 4.4 sends warnings if MISSION_ITEM used
+// ArduPilot 4.8 stops compiling in MISSION_ITEM but still sends warnings
+// ArduPilot 4.9 removes the code but sends message about MISSION_ITEM not supported
+// ArduPilot 4.10 stops sending the warning
 #ifndef AP_MAVLINK_MSG_MISSION_REQUEST_ENABLED
 #define AP_MAVLINK_MSG_MISSION_REQUEST_ENABLED AP_MISSION_ENABLED
 #endif