package/cdrkit: clean {HOST_, }CDRKIT_CONF_OPT

Extending {C,LD}FLAGS for both host and target cdrkit package is not needed
because it is already handled by the {host-,}cmake-package infrastructure.

Signed-off-by: Samuel Martin <s.martin49@gmail.com>
Signed-off-by: Peter Korsgaard <peter@korsgaard.com>