Revert "Skip test_dhcp_lease_served_when_dhcp_agent_down due to bug"

This reverts commit 9403e5b97a.

Reason for revert: The bug was resolved with
https://review.opendev.org/c/openstack/neutron/+/967808

Related-Bug: #2131801

Change-Id: If0235cd176ca33e46c363809d9f700d75a610796

zuul.d/devstack-tobiko-neutron.yaml

@@ -94,8 +94,5 @@
     voting: true
     description: |
       Base Tobiko devstack job to execute scenario+faults+scenario test cases.
-    vars:
-      <<: *FAULTS_VARS
-      # TODO(eolivare): remove the skip when #2131801 is fixed
-      pytest_addopts_global: "--skipregex=test_dhcp_lease_served_when_dhcp_agent_down"
+    vars: *FAULTS_VARS
     irrelevant-files: *FAULTS_IRRELEVANT_FILES

zuul.d/devstack-tobiko-ovs.yaml

@@ -79,5 +79,3 @@
       devstack_plugins:
         neutron: "https://opendev.org/openstack/neutron"
         designate: https://opendev.org/openstack/designate.git
-      # TODO(eolivare): remove the skip when #2131801 is fixed
-      pytest_addopts_global: "--skipregex=test_dhcp_lease_served_when_dhcp_agent_down"