openvswitch.spec: Remove dependency with openvswitch-kmod.

Upstream Linux has OVS kernel module that includes most (not all) of
the features that comes with the kernel module from openvswitch.org.
So, it is okay to relax the requirement for OVS userspace package
to depend on openvswitch-kmod package.

Signed-off-by: Gurucharan Shetty <gshetty@nicira.com>
Acked-by: Ben Pfaff <blp@nicira.com>