Deprecate --gfe2_reloadable_flag_quic_check_cid_collision_when_issue_new_cid

This change is blocking cr/538258005

PiperOrigin-RevId: 538842417
diff --git a/quiche/quic/core/quic_connection_test.cc b/quiche/quic/core/quic_connection_test.cc
index c501347..00f02b2 100644
--- a/quiche/quic/core/quic_connection_test.cc
+++ b/quiche/quic/core/quic_connection_test.cc
@@ -14199,11 +14199,7 @@
         .WillOnce(Return(TestConnectionId(456)));
   }
   EXPECT_CALL(visitor_, MaybeReserveConnectionId(_)).WillOnce(Return(false));
-  if (GetQuicReloadableFlag(quic_check_cid_collision_when_issue_new_cid)) {
-    EXPECT_CALL(visitor_, SendNewConnectionId(_)).Times(0);
-  } else {
-    EXPECT_CALL(visitor_, SendNewConnectionId(_)).Times(1);
-  }
+  EXPECT_CALL(visitor_, SendNewConnectionId(_)).Times(0);
   connection_.MaybeSendConnectionIdToClient();
 }