Remove unused PROMETHEUS_RATE_DURATION

It was replaced by the QUERY environment in [1].

[1] afe631a2d0335a010f8f784b144f37305ece0147

Change-Id: I6e5780f93036c852c1de0aeef1eb68f41855838b
Signed-off-by: Takashi Kajinami <kajinamit@oss.nttdata.com>
diff --git a/telemetry_tempest_plugin/scenario/test_telemetry_integration_prometheus.py b/telemetry_tempest_plugin/scenario/test_telemetry_integration_prometheus.py
index 6f9e3f6..1def0f6 100644
--- a/telemetry_tempest_plugin/scenario/test_telemetry_integration_prometheus.py
+++ b/telemetry_tempest_plugin/scenario/test_telemetry_integration_prometheus.py
@@ -166,7 +166,6 @@
             "NEUTRON_NETWORK": self.stack_network_id,
             "STACK_NAME": self.stack_name,
             "RESOURCE_PREFIX": resource_prefix,
-            "PROMETHEUS_RATE_DURATION": str(prometheus_rate_duration),
             "LOAD_LENGTH": str(prometheus_rate_duration * 2),
             "QUERY": query,
         })