labs: remove redundant variable setting
labs: remove redundant variable setting

In setup_neutron_network, nsdhcp is set twice. Remove the second,
redundant instance.

Change-Id: I677d8d76632a4a70c22830b79b93da705c033a58

harrisonfeng/training-guides,openstack/training-guides,Nabs007/training-guides,Nabs007/training-guides,Nabs007/training-guides,harrisonfeng/training-guides,openstack/training-guides,harrisonfeng/training-guides