Remove a redundant KeyPairsV3ClientJSON

There are duplicated KeyPairsV3ClientJSON settings in __init__()
of Manager class. This patch removes it.

Change-Id: Ia19e8db43d601c7ca919820c62da699e660e0623
diff --git a/tempest/clients.py b/tempest/clients.py
index 19b4e11..aebf766 100644
--- a/tempest/clients.py
+++ b/tempest/clients.py
@@ -307,8 +307,6 @@
             self.servers_v3_client = ServersV3ClientJSON(self.auth_provider)
             self.limits_client = LimitsClientJSON(self.auth_provider)
             self.images_client = ImagesClientJSON(self.auth_provider)
-            self.keypairs_v3_client = KeyPairsV3ClientJSON(
-                self.auth_provider)
             self.keypairs_client = KeyPairsClientJSON(self.auth_provider)
             self.keypairs_v3_client = KeyPairsV3ClientJSON(
                 self.auth_provider)