Remove dead code in MASQUE

PiperOrigin-RevId: 391056800
diff --git a/quic/masque/masque_server_session.cc b/quic/masque/masque_server_session.cc
index effc17f..575ac9f 100644
--- a/quic/masque/masque_server_session.cc
+++ b/quic/masque/masque_server_session.cc
@@ -196,7 +196,6 @@
     }
     if (scheme.empty()) {
       return CreateBackendErrorResponse("400", "Empty scheme");
-      return nullptr;
     }
     if (method != "CONNECT-UDP") {
       QUIC_DLOG(ERROR) << "MASQUE request with bad method \"" << method << "\"";