Remove legacy-centos-7-4-node nodeset
Remove legacy-centos-7-4-node nodeset

We have no jobs using this nodeset, lets remove it.

Change-Id: Ib5a70c1a71a3d83e504b5c6caaf60c4e71bc6e68
Signed-off-by: Paul Belanger <e7139c8e6c4ea75cc1c287ce081b2dc0f3ab39ec@redhat.com>

openstack-infra/openstack-zuul-jobs,openstack-infra/openstack-zuul-jobs