Remove test duplication between tempest and n-t-p RoutersDVRTest

RoutersDVRTest -https://opendev.org/openstack/tempest/src/branch\
/master/tempest/api/network/admin/test_routers_dvr.py has same
functionality in tempest and neutron-tempest-plugin, so with
removing these tests from tempest we can get rid of whole module,
reducing the test duplications.

Change-Id: Ie7d37def794a3cbdb2444ebbeba237fd58ddfb8a
1 file changed