Remove unused client in ServerMetadataTestJSON

cls.quota is not used so can be removed.
Besides, to use "quotas" as alias of "quotas_client" seems
not a good idea

Change-Id: I3b7ef95dbbdb0b95c7e5ec8ce8de5f03d3bcee6b
diff --git a/tempest/api/compute/servers/test_server_metadata.py b/tempest/api/compute/servers/test_server_metadata.py
index cb66e81..847b7a1 100644
--- a/tempest/api/compute/servers/test_server_metadata.py
+++ b/tempest/api/compute/servers/test_server_metadata.py
@@ -23,7 +23,6 @@
     def setup_clients(cls):
         super(ServerMetadataTestJSON, cls).setup_clients()
         cls.client = cls.servers_client
-        cls.quotas = cls.quotas_client
 
     @classmethod
     def resource_setup(cls):
diff --git a/tempest/api/compute/servers/test_server_metadata_negative.py b/tempest/api/compute/servers/test_server_metadata_negative.py
index aae9101..62b8962 100644
--- a/tempest/api/compute/servers/test_server_metadata_negative.py
+++ b/tempest/api/compute/servers/test_server_metadata_negative.py
@@ -25,7 +25,6 @@
     def setup_clients(cls):
         super(ServerMetadataNegativeTestJSON, cls).setup_clients()
         cls.client = cls.servers_client
-        cls.quotas = cls.quotas_client
 
     @classmethod
     def resource_setup(cls):
@@ -134,7 +133,8 @@
         # A 403 Forbidden or 413 Overlimit (old behaviour) exception
         # will be raised while exceeding metadata items limit for
         # tenant.
-        quota_set = self.quotas.show_quota_set(self.tenant_id)['quota_set']
+        quota_set = self.quotas_client.show_quota_set(
+            self.tenant_id)['quota_set']
         quota_metadata = quota_set['metadata_items']
         if quota_metadata == -1:
             raise self.skipException("No limit for metadata_items")