Mantis: move tap_esc to extras

This way we work around an issue where tap_esc got stuck during bootup
in a cold boot.

boards/atl/mantis-edu/init/rc.board_defaults

@@ -29,20 +29,3 @@ set MIXER_FILE ""
 set MIXER "skip"
 set OUTPUT_MODE "skip"
 
-# Start ESC already here, so that we have beeps.
-tap_esc start -d /dev/ttyS4 -n 4
-
-# Transition from previous non open-source flight stack
-if param compare SYS_AUTOSTART 4001
-then
-	param reset_all
-	tune_control play -t 4
-	sleep 2
-	if bl_update /etc/extras/bootloader.bin
-	then
-		tune_control play -t 3
-	else
-		tune_control play -t 5
-	fi
-	sleep 2
-fi

boards/atl/mantis-edu/init/rc.board_extras

@@ -0,0 +1,18 @@
+#!/bin/sh
+
+tap_esc start -d /dev/ttyS4 -n 4
+
+# Transition from previous non open-source flight stack
+if param compare SYS_AUTOSTART 4001
+then
+	param reset_all
+	tune_control play -t 4
+	sleep 2
+	if bl_update /etc/extras/bootloader.bin
+	then
+		tune_control play -t 3
+	else
+		tune_control play -t 5
+	fi
+	sleep 2
+fi