package/*: remove useless explicit set of function returncode

somebody started to set a function returncode in the validation
stuff and everybody copies it, e.g.

myfunction()
{
	fire_command

	return $?
}

a function automatically returns with the last returncode,
so we can safely remove the command 'return $?'. reference:

http://tldp.org/LDP/abs/html/exit-status.html


"The last command executed in the function or script determines the exit status."

Signed-off-by: Bastian Bittorf <bittorf@bluebottle.com>

Backport of r42278

git-svn-id: svn://svn.openwrt.org/openwrt/branches/barrier_breaker@42379 3c298f89-4303-0410-b956-a3cf2f4a3e73