cyrus-sasl: remove the unnecessary pkg_postinst

saslpasswd2 is used by an administrator to set a user's sasl password,
setting a default one in pkg_postinst in not only unnecessary but also
inappropriate.

Besides, running saslpasswd2 takes a significant amount of time to finish,
so this pkg_postinst will make the first boot take longer time.

According to the above two reasons, the patch remove the pkg_postint.

Signed-off-by: Chen Qi <Qi.Chen@windriver.com>
Signed-off-by: Joe MacDonald <joe@deserted.net>