run-postinsts: remove the init script after a clean start-up

run-postinsts: remove the init script after a clean start-up

If we enable ipk/deb package back-end, and we have 'package-management'
in our IMAGE_FEATURES, then the /etc/rcS.d/S99run-postinsts would
still exist in our system after a clean start-up.

The initial design for run-postinsts requires the related init script
to be removed if there's no more post-install script left in the system.

This patch fixes this problem.

[YOCTO #5718]

(From OE-Core rev: 08a2f48cb95256c6d44c8574949fabafe1466969)

Signed-off-by: Chen Qi <Qi.Chen@windriver.com>
Signed-off-by: Saul Wold <sgw@linux.intel.com>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>