scripts: extend rstrip.sh to remove bad rpaths

Remove all rpath entries which do not point to a location below /lib or
/usr/lib and which do not begin with '$ORIGIN'.

Signed-off-by: Jo-Philipp Wich <jow@openwrt.org>

git-svn-id: svn://svn.openwrt.org/openwrt/trunk@44377 3c298f89-4303-0410-b956-a3cf2f4a3e73