remove mongodb 1.8 version since manifest does not contain 1.8 version

Change-Id: I7600e3b49d8df90d5c71a993cec39ce09393c31f
Reviewed-on: http://reviews.cloudfoundry.org/13669
Tested-by: CI Master <cf-ci@rbcon.com>
Reviewed-by: Felix Hu <hhu@vmware.com>
Reviewed-by: Nicholas Kushmerick <nicholask@vmware.com>