msg: purge unused qshell

msg/CMakeLists.txt

@@ -119,8 +119,6 @@ set(msg_files
 	power_monitor.msg
 	pwm_input.msg
 	px4io_status.msg
-	qshell_req.msg
-	qshell_retval.msg
 	radio_status.msg
 	rate_ctrl_status.msg
 	rc_channels.msg

msg/qshell_req.msg

@@ -1,5 +0,0 @@
-uint64 timestamp		# time since system start (microseconds)
-char[100] cmd
-uint32 MAX_STRLEN = 100
-uint32 strlen
-uint32 request_sequence

msg/qshell_retval.msg

@@ -1,3 +0,0 @@
-uint64 timestamp		# time since system start (microseconds)
-int32 return_value
-uint32 return_sequence