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_simple_server_session.cc b/quic/tools/quic_simple_server_session.cc
index c60a9e2..aa13a5b 100644
--- a/quic/tools/quic_simple_server_session.cc
+++ b/quic/tools/quic_simple_server_session.cc
@@ -39,7 +39,7 @@
 }
 
 QuicSimpleServerSession::~QuicSimpleServerSession() {
-  delete connection();
+  DeleteConnection();
 }
 
 QuicCryptoServerStreamBase*