Remove unused QuicDispatcher.session_map_.

PiperOrigin-RevId: 387601903
diff --git a/quic/core/quic_dispatcher.h b/quic/core/quic_dispatcher.h
index 7020c8c..a6ba1a6 100644
--- a/quic/core/quic_dispatcher.h
+++ b/quic/core/quic_dispatcher.h
@@ -121,10 +121,6 @@
   void OnConnectionAddedToTimeWaitList(
       QuicConnectionId server_connection_id) override;
 
-  using SessionMap = absl::flat_hash_map<QuicConnectionId,
-                                         std::unique_ptr<QuicSession>,
-                                         QuicConnectionIdHash>;
-
   using ReferenceCountedSessionMap =
       absl::flat_hash_map<QuicConnectionId,
                           std::shared_ptr<QuicSession>,
@@ -132,8 +128,6 @@
 
   size_t NumSessions() const;
 
-  const SessionMap& session_map() const { return session_map_; }
-
   // Deletes all sessions on the closed session list and clears the list.
   virtual void DeleteSessions();
 
@@ -420,7 +414,6 @@
   // The list of connections waiting to write.
   WriteBlockedList write_blocked_list_;
 
-  SessionMap session_map_;
   ReferenceCountedSessionMap reference_counted_session_map_;
 
   // Entity that manages connection_ids in time wait state.