Remove unnecessary resource_setup()

Since I82b216844b43f3440d1827e66225f1f97e97dd19 , resource_setup()
became useless, so there is no need to keep it, just remove it for
the code clean.

Change-Id: Ib187ce91f2d3d629389fa0581bd051659d551658

tempest/api/volume/test_volumes_backup.py

@@ -30,10 +30,6 @@ class VolumesBackupsV2Test(base.BaseVolumeTest):
         if not CONF.volume_feature_enabled.backup:
             raise cls.skipException("Cinder backup feature disabled")
 
-    @classmethod
-    def resource_setup(cls):
-        super(VolumesBackupsV2Test, cls).resource_setup()
-
     @test.idempotent_id('a66eb488-8ee1-47d4-8e9f-575a095728c6')
     def test_volume_backup_create_get_detailed_list_restore_delete(self):
         # Create backup