aarch64: vp8: Remove superfluous includes

This fixes building with MSVC, which lacks unistd.h.

Signed-off-by: Martin Storsjö <martin@martin.st>
(cherry picked from commit ad32f7b126)

libavcodec/aarch64/vp8dsp_init_aarch64.c

@@ -17,10 +17,6 @@
  */
 
 #include <stdint.h>
-#include <string.h>
-#include <stdio.h>
-#include <stdlib.h>
-#include <unistd.h>
 
 #include "libavutil/attributes.h"
 #include "libavutil/aarch64/cpu.h"