bhyve: remove redundant code that adds "template" netdev name

bhyve: remove redundant code that adds "template" netdev name

The FreeBSD version of virNetDevTapCreate() now calls
virNetDevGenerateName(), and virNetDevGenerateName() understands that
a blank ifname should be replaced with a generated name based on a
device-type-specific template - so there is no longer any need for the
higher level functions to stuff a template name ("vnet%d") into
ifname.

Signed-off-by: Laine Stump <laine@redhat.com>
Reviewed-by: Michal Privoznik <mprivozn@redhat.com>