system/inittab: update to fix bug #7442

Update inittabs (skeleton/busybox & sysvinit) to remove the trailing
REMOUNT_ROOTFS_RW comment used as magic string in system/system.mk to
enable/disable remounting the root filesystem rw or not since it affects
sysvinit in doing so properly as reported in bug #7442.

Instead update the sed expressions to match clean non-commented strings
by searching for "-o remount,rw /" and checking that's the end of the
line as well to avoid affecting possibly other remounts that a user can
have in a custom inittab.

Long-term the startup block of inittab should just move to a S00sysinit
script or similar so that rcS can pick it up directly.

Signed-off-by: Gustavo Zacarias <gustavo@zacarias.com.ar>
Reviewed-by: "Yann E. MORIN" <yann.morin.1998@free.fr>
Signed-off-by: Peter Korsgaard <peter@korsgaard.com>