cve-update-nvd2-native: Remove duplicated CVE_CHECK_DB_FILE definition

cve-update-nvd2-native: Remove duplicated CVE_CHECK_DB_FILE definition

CVE_CHECK_DB_FILE is already defined in cve-check.bbclass which is
always inherited in cve-update-nvd2-native (There is a check line 40).

Remove it to avoid confusion. Otherwise, this should not change
anything.

Signed-off-by: Yoann Congal <yoann.congal@smile.fr>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>
(cherry picked from commit e5f3f223885c17b7007c310273fc7c80b90a4105)
Signed-off-by: Steve Sakoman <steve@sakoman.com>