Removes duplicate flag for token_format.

The token_format settings defaults to PKI, but both the
"PKI" and "UUID" lines were still in the sample config file.
This patch removes the duplicate and leaves only the
correct default.

Change-Id: Ib8560952ec2aee6d6b6eda944c6ec1f96fdc5c4c

etc/keystone.conf.sample

@@ -92,14 +92,13 @@
 #cert_required = True
 
 [signing]
-#token_format = UUID
+#token_format = PKI
 #certfile = /etc/keystone/ssl/certs/signing_cert.pem
 #keyfile = /etc/keystone/ssl/private/signing_key.pem
 #ca_certs = /etc/keystone/ssl/certs/ca.pem
 #key_size = 1024
 #valid_days = 3650
 #ca_password = None
-#token_format = PKI
 
 [ldap]
 # url = ldap://localhost