QBONE Server Simulator: Minor shutdown crash fix

Had been CHECK-confirming cleanup of the event loop before server destruction, but I later changed it to defer that cleanup due to some multi-thread interactions so that CHECK was always firing on shutdown.

PiperOrigin-RevId: 930039423

quiche/quic/qbone/test_tools/basic_quic_server.cc

diff --git a/quiche/quic/qbone/test_tools/basic_quic_server.cc b/quiche/quic/qbone/test_tools/basic_quic_server.cc
index 00d58bf..8e1fdb1 100644
--- a/quiche/quic/qbone/test_tools/basic_quic_server.cc
+++ b/quiche/quic/qbone/test_tools/basic_quic_server.cc
@@ -277,7 +277,6 @@
     QUICHE_CHECK(!running_notification_.HasBeenNotified() ||
                  shutdown_notification_.HasBeenNotified());
     QUICHE_CHECK(!dispatcher_);
-    QUICHE_CHECK(!event_loop_);
   }
 
   void Run() override {