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/core/quic_session_test.cc b/quic/core/quic_session_test.cc
index 4603d6c..5c04379 100644
--- a/quic/core/quic_session_test.cc
+++ b/quic/core/quic_session_test.cc
@@ -170,9 +170,7 @@
         std::make_unique<NullEncrypter>(connection->perspective()));
   }
 
-  ~TestSession() override {
-    delete connection();
-  }
+  ~TestSession() override { DeleteConnection(); }
 
   TestCryptoStream* GetMutableCryptoStream() override {
     return &crypto_stream_;