Remove unused add_sample()

add_sample() has been added since I08c9b6a02bcddd8cab2d066928513b4ae40431ec ,
but we never use this metod over 2 years.
So this patch removes the method for cleanup.

Change-Id: I340d96c27f0e906df5b8a109494920e9cd3b21d1
diff --git a/tempest/services/telemetry/json/telemetry_client.py b/tempest/services/telemetry/json/telemetry_client.py
index 05530b1..abdeba2 100644
--- a/tempest/services/telemetry/json/telemetry_client.py
+++ b/tempest/services/telemetry/json/telemetry_client.py
@@ -30,17 +30,6 @@
     def serialize(self, body):
         return json.dumps(body)
 
-    def add_sample(self, sample_list, meter_name, meter_unit, volume,
-                   sample_type, resource_id, **kwargs):
-        sample = {"counter_name": meter_name, "counter_unit": meter_unit,
-                  "counter_volume": volume, "counter_type": sample_type,
-                  "resource_id": resource_id}
-        for key in kwargs:
-            sample[key] = kwargs[key]
-
-        sample_list.append(self.serialize(sample))
-        return sample_list
-
     def create_sample(self, meter_name, sample_list):
         uri = "%s/meters/%s" % (self.uri_prefix, meter_name)
         body = self.serialize(sample_list)