check whether there is socket to delete

for no_simbricks experiments

experiments/simbricks/experiments.py

@@ -292,8 +292,10 @@ class ExperimentBaseRunner(object):
             scs = []
             for (exec,sock) in self.sockets:
                 scs.append(exec.rmtree(sock))
+            if len(scs):
                 await asyncio.wait(scs)
             
+
             # add all simulator components to the output
             for sim,sc in self.running:
                 self.out.add_sim(sim, sc)