Remove battery_warning_init.sh.

shell_scripts/battery_warning_init.sh
	-Remove the `battery_warning_init.sh`, which was called by
	`cron` minutely and checked if `battery_warningd.py` was
	running; if not, it started it.
	-Opting for a solution that kicks off the battery-checker on
	boot from `/etc/rc.local`, which is cleaner (also, there isn't
	any danger of the checker dying at some point during execution).