avformat/webm_chunk: Remove superfluous headers

libavutil/avstring.h is unnecessary since 8a632b3e. The other
unnecessary headers were never used.
Signed-off-by: Andreas Rheinhardt <andreas.rheinhardt@gmail.com>

libavformat/webm_chunk.c

@@ -24,23 +24,14 @@
  * chunk, followed by data chunks where each Cluster is written out as a Chunk.
  */
 
-#include <float.h>
-#include <time.h>
-
 #include "avformat.h"
 #include "avio.h"
 #include "avio_internal.h"
 #include "internal.h"
 
-#include "libavutil/avassert.h"
 #include "libavutil/log.h"
 #include "libavutil/opt.h"
-#include "libavutil/avstring.h"
-#include "libavutil/parseutils.h"
 #include "libavutil/mathematics.h"
-#include "libavutil/time.h"
-#include "libavutil/time_internal.h"
-#include "libavutil/timestamp.h"
 
 #define MAX_FILENAME_SIZE 1024