Update aggregator.py

Signed-off-by: Parth Mandaliya <parthx.mandaliya@intel.com>

openfl/interface/aggregator.py

@@ -3,8 +3,6 @@
 """Aggregator module."""
 
 import sys
-import threading
-
 from logging import getLogger
 
 from click import echo
@@ -56,12 +54,7 @@ def start_(plan, authorized_cols, secure):
 
     logger.info('🧿 Starting the Aggregator Service.')
 
-    agg_server = plan.get_server()
-
-    plan.aggregator_.agg_grpc_server_start = threading.Thread(target=agg_server.serve)
-    plan.aggregator_.start_flow_execution = threading.Thread(target=plan.aggregator_.run_flow_until_transition)
-    plan.aggregator_.agg_grpc_server_start.start()
-    plan.aggregator_.start_flow_execution.start()
+    plan.get_server().serve()
 
 
 @aggregator.command(name='generate-cert-request')