Remove unused global variable from VolumesV1NegativeTest class

Change-Id: I5d4a0e30f07ad13a7f478a7ca7900ca999f7333c
diff --git a/tempest/api/volume/test_volumes_negative.py b/tempest/api/volume/test_volumes_negative.py
index d2c05ae..16c8571 100755
--- a/tempest/api/volume/test_volumes_negative.py
+++ b/tempest/api/volume/test_volumes_negative.py
@@ -299,4 +299,3 @@
 
 class VolumesV1NegativeTest(VolumesV2NegativeTest):
     _api_version = 1
-    _name = 'display_name'