lavfi: Drop unused and empty header file

This header was public but deprecated on 2013-04-11 (lavfi 3.8.0).

libavfilter/Makefile

@@ -2,7 +2,6 @@ NAME = avfilter
 DESC = Libav video filtering library
 
 HEADERS = avfilter.h                                                    \
-          avfiltergraph.h                                               \
           buffersink.h                                                  \
           buffersrc.h                                                   \
           version.h                                                     \

libavfilter/avfiltergraph.h

@@ -1,29 +0,0 @@
-/*
- * Filter graphs
- * copyright (c) 2007 Bobby Bingham
- *
- * This file is part of Libav.
- *
- * Libav is free software; you can redistribute it and/or
- * modify it under the terms of the GNU Lesser General Public
- * License as published by the Free Software Foundation; either
- * version 2.1 of the License, or (at your option) any later version.
- *
- * Libav is distributed in the hope that it will be useful,
- * but WITHOUT ANY WARRANTY; without even the implied warranty of
- * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
- * Lesser General Public License for more details.
- *
- * You should have received a copy of the GNU Lesser General Public
- * License along with Libav; if not, write to the Free Software
- * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA
- */
-
-#ifndef AVFILTER_AVFILTERGRAPH_H
-#define AVFILTER_AVFILTERGRAPH_H
-
-#include "avfilter.h"
-#include "libavutil/log.h"
-
-
-#endif /* AVFILTER_AVFILTERGRAPH_H */