Mantis: remove startup tune volume

Let's just leave it at the default like the rest of the beeps.

ROMFS/px4fmu_common/init.d/airframes/4061_atl_mantis_edu

@@ -173,6 +173,5 @@ param set-default SENS_FLOW_MINHGT 0.15
 param set-default SENS_FLOW_MAXHGT 5.0
 param set-default SENS_FLOW_ROT    0
 
-# ignore the SD card errors and use normal startup sound, and make it less loud
+# ignore the SD card errors and use normal startup sound
 set STARTUP_TUNE "1"
-set STARTUP_TUNE_VOLUME "-s 20"

ROMFS/px4fmu_common/init.d/rcS

@@ -49,7 +49,6 @@ set SDCARD_EXT_PATH /fs/microsd/ext_autostart
 set SDCARD_FORMAT no
 set SDCARD_MIXERS_PATH /fs/microsd/etc/mixers
 set STARTUP_TUNE 1
-set STARTUP_TUNE_VOLUME ""
 set USE_IO no
 set VEHICLE_TYPE none
 set DATAMAN_ARGS ""
@@ -485,7 +484,7 @@ else
 	param compare CBRK_BUZZER 782090
 	if [ "$?" != "0" -o "$STARTUP_TUNE" != "1" ]
 	then
-		tune_control play -t $STARTUP_TUNE $STARTUP_TUNE_VOLUME
+		tune_control play -t $STARTUP_TUNE
 	fi
 
 	#
@@ -604,7 +603,6 @@ unset SDCARD_EXT_PATH
 unset SDCARD_FORMAT
 unset SDCARD_MIXERS_PATH
 unset STARTUP_TUNE
-unset STARTUP_TUNE_VOLUME
 unset USE_IO
 unset VEHICLE_TYPE
 unset DATAMAN_ARGS