Update l3_centralizedattackdetectorClient.py

src/l3_centralizedattackdetector/client/l3_centralizedattackdetectorClient.py

 import grpc, logging
 from common.tools.client.RetryDecorator import retry, delay_exponential
-from l3_centralizedattackdetector.proto.context_pb2 import Empty
 from l3_centralizedattackdetector.proto.l3_centralizedattackdetector_pb2_grpc import (
     L3CentralizedattackdetectorStub,
 )