matroskadec: remove unused struct name

Originally committed as revision 14578 to svn://svn.ffmpeg.org/ffmpeg/trunk

libavformat/matroskadec.c

@@ -168,12 +168,12 @@ typedef struct {
     uint64_t pos;
 } MatroskaSeekhead;
 
-typedef struct MatroskaLevel {
+typedef struct {
     uint64_t start;
     uint64_t length;
 } MatroskaLevel;
 
-typedef struct MatroskaDemuxContext {
+typedef struct {
     AVFormatContext *ctx;
 
     /* ebml stuff */