Delete not-useful flaky integ test (#3569)

Deleting an old smoke test from this package since it has been consistently flaky.  The service team confirmed this is due to a noisy neighbor.

Author: SamRemis

tests/integration/test_smoke.py

@@ -89,7 +89,6 @@
     'sns': {'ListTopics': {}},
     'sqs': {'ListQueues': {}},
     'ssm': {'ListDocuments': {}},
-    'storagegateway': {'ListGateways': {}},
     # sts tests would normally go here, but
     # there aren't any calls you can make when
     # using session credentials so we don't run any