tests: do not write to maybe-closed socket

The agent might exit before the empty MSG_DATA_STDIN message is sent.

Author: DemiMarie

qrexec/tests/socket/agent.py

@@ -532,7 +532,6 @@ def test_exec_service_bad_multiplexer(self):
 
     def _test_exec_service_fail(self, exit_code=qrexec.QREXEC_EXIT_PROBLEM):
         target, dom0 = self.execute_qubesrpc("qubes.Service+arg", "domX")
-        target.send_message(qrexec.MSG_DATA_STDIN, b"")
         messages = target.recv_all_messages()
         self.assertListEqual(
             util.sort_messages(messages),