lavf: Remove a redundant include of sys/stat.h

The same file already includes this header a few lines further
above.
Signed-off-by: NMartin Storsjö <martin@martin.st>

libavformat/os_support.h

@@ -48,8 +48,6 @@
 #include <io.h>
 #endif
 #define mkdir(a, b) _mkdir(a)
-#else
-#include <sys/stat.h>
 #endif
 
 static inline int is_dos_path(const char *path)