Updating code to PuTTY 64f8f68a (by removing an unused declaration)

Source commit: 4d772569cd89d44f096afbc9e9afd81e037a3763

source/putty/putty.h

@@ -2052,7 +2052,6 @@ void queue_toplevel_callback(CALLBACK_SET toplevel_callback_fn_t fn, void *ctx);
 int run_toplevel_callbacks(CALLBACK_SET_ONLY);
 int toplevel_callback_pending(CALLBACK_SET_ONLY);
 struct callback_set * get_callback_set(Plug * plug);
-struct callback_set * get_frontend_callback_set(Frontend * frontend);
 struct callback_set * get_seat_callback_set(Seat * seat);
 void delete_callbacks_for_context(CALLBACK_SET void *ctx);
 LogPolicy *log_get_logpolicy(LogContext *ctx); // WINSCP