Remove unnessary delete_volume in test_volumes_list

In test_volumes_list.py, it calles cls.create_volume to
create 3 test volumes, and volumes created by cls.create_volume
will be automatically cleaned by base's clear_volumes() in
base's resource_cleanup, so this is to remove the unnecessary
delete_volume

Change-Id: I763cb6cc66cebab7601846c2009676c20a8d1fdd
diff --git a/tempest/api/volume/v2/test_volumes_list.py b/tempest/api/volume/v2/test_volumes_list.py
index 1fdcb49..c501ffc 100644
--- a/tempest/api/volume/v2/test_volumes_list.py
+++ b/tempest/api/volume/v2/test_volumes_list.py
@@ -42,22 +42,13 @@
         super(VolumesV2ListTestJSON, cls).resource_setup()
 
         # Create 3 test volumes
-        cls.volume_list = []
         cls.volume_id_list = []
         cls.metadata = {'Type': 'work'}
         for i in range(3):
             volume = cls.create_volume(metadata=cls.metadata)
             volume = cls.client.show_volume(volume['id'])['volume']
-            cls.volume_list.append(volume)
             cls.volume_id_list.append(volume['id'])
 
-    @classmethod
-    def resource_cleanup(cls):
-        # Delete the created volumes
-        for volid in cls.volume_id_list:
-            cls.delete_volume(cls.client, volid)
-        super(VolumesV2ListTestJSON, cls).resource_cleanup()
-
     @test.idempotent_id('2a7064eb-b9c3-429b-b888-33928fc5edd3')
     def test_volume_list_details_with_multiple_params(self):
         # List volumes detail using combined condition