flat network type is not mandatory. There are two cases,
1. ironic with flat network: we can use neutron vlan network to
provision baremetal nodes, as long as the interface of the baremetal
nodes are configured to use the same vlan.
2. ironic with neutron network: all provision and cleaning_network can
be vlan type and no flat is needed at all.
So we should remove the task.
Change-Id: I176ded6d2a8b14e350f665f63bc37eb488d32679
Closes-Bug: #1725170