commander: remove set but unused HITL flag

This flag does not seem to be used anywhere.

msg/vehicle_control_mode.msg

@@ -3,9 +3,6 @@ bool flag_armed			# is set whenever the writing thread stores new data
 
 bool flag_external_manual_override_ok		# external override non-fatal for system. Only true for fixed wing
 
-# XXX needs yet to be set by state machine helper
-bool flag_system_hil_enabled
-
 bool flag_control_manual_enabled		# true if manual input is mixed in
 bool flag_control_auto_enabled			# true if onboard autopilot should act
 bool flag_control_offboard_enabled		# true if offboard control should be used

src/modules/commander/Commander.cpp

@@ -3171,7 +3171,6 @@ set_control_mode()
 	/* set vehicle_control_mode according to set_navigation_state */
 	control_mode.flag_armed = armed.armed;
 	control_mode.flag_external_manual_override_ok = (!status.is_rotary_wing && !status.is_vtol);
-	control_mode.flag_system_hil_enabled = status.hil_state == vehicle_status_s::HIL_STATE_ON;
 	control_mode.flag_control_offboard_enabled = false;
 
 	switch (status.nav_state) {