msg/geofence_update.msg: remove this topic

We'll use dataman to check for geofence data updates.

msg/CMakeLists.txt

@@ -59,7 +59,6 @@ set(msg_file_names
 	follow_target.msg
 	fw_pos_ctrl_status.msg
 	geofence_result.msg
-	geofence_update.msg
 	gps_dump.msg
 	gps_inject_data.msg
 	hil_sensor.msg

msg/geofence_update.msg

@@ -1,4 +0,0 @@
-# This message is used to notify the system about a geofence update (dataman
-# storage)
-
-uint32 dummy       # unused