Stop using "delete connection()" in QuicSession classes and use DeleteConnection() instead, which prevents double deletion and sets connection_ to nullptr.

gfe-relnote: n/a (Set deleted pointer to nullptr)
PiperOrigin-RevId: 284764494
Change-Id: I6d7f36768e14f06b9cd8267ac74d22d189463579
diff --git a/quic/tools/quic_transport_simple_server_session.cc b/quic/tools/quic_transport_simple_server_session.cc
index 60cedd5..b1221ae 100644
--- a/quic/tools/quic_transport_simple_server_session.cc
+++ b/quic/tools/quic_transport_simple_server_session.cc
@@ -147,7 +147,7 @@
 
 QuicTransportSimpleServerSession::~QuicTransportSimpleServerSession() {
   if (owns_connection_) {
-    delete connection();
+    DeleteConnection();
   }
 }