Disabling the lights on raspberry pi has been documented a number of times on the web.
If differs from model to model, however the following method just sets the brightness to zero and should work on all models.

Modify your /etc/rc.local too like the following

#!/bin/sh -e
#
# rc.local
#
# This script is executed at the end of each multiuser runlevel.
# Make sure that the script will "exit 0" on success or any other
# value on error.
#
# In order to enable or disable this script just change the execution
# bits.
#
# By default this script does nothing.

# Print the IP address
_IP=$(hostname -I) || true
if [ "$_IP" ]; then
  printf "My IP address is %s\n" "$_IP"
fi

echo 0 > /sys/class/leds/led1/brightness
echo 0 > /sys/class/leds/led0/brightness

exit 0