Disable database support in linux-pam

Due to the conflicts with default Berkeley DB configuration, disable
database support in linux-pam: pam_userdb is not built.

Signed-off-by: Dmitry <golubovsky@gmail.com>
Acked-by: Arnout Vandecappelle (Essensium/Mind) <arnout@mind.be>
Signed-off-by: Peter Korsgaard <jacmet@sunsite.dk>