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/test_tools/quic_test_utils.cc b/quic/test_tools/quic_test_utils.cc
index 8099c34..156d00e 100644
--- a/quic/test_tools/quic_test_utils.cc
+++ b/quic/test_tools/quic_test_utils.cc
@@ -553,7 +553,7 @@
 }
 
 MockQuicSession::~MockQuicSession() {
-  delete connection();
+  DeleteConnection();
 }
 
 QuicCryptoStream* MockQuicSession::GetMutableCryptoStream() {
@@ -624,7 +624,7 @@
 }
 
 MockQuicSpdySession::~MockQuicSpdySession() {
-  delete connection();
+  DeleteConnection();
 }
 
 QuicCryptoStream* MockQuicSpdySession::GetMutableCryptoStream() {
@@ -657,7 +657,7 @@
 }
 
 TestQuicSpdyServerSession::~TestQuicSpdyServerSession() {
-  delete connection();
+  DeleteConnection();
 }
 
 QuicCryptoServerStreamBase*