Revert "avfilter/stack_internal: add missing header includes"

This reverts commit 205117d8.

This didn't fix make checkheaders after all, and also broke compilation in some
scenarios.
Signed-off-by: James Almer <jamrial@gmail.com>

libavfilter/Makefile

@@ -629,7 +629,7 @@ SKIPHEADERS-$(CONFIG_LIBVIDSTAB)             += vidstabutils.h
 
 SKIPHEADERS-$(CONFIG_QSVVPP)                 += qsvvpp.h
 SKIPHEADERS-$(CONFIG_OPENCL)                 += opencl.h
-SKIPHEADERS-$(CONFIG_VAAPI)                  += vaapi_vpp.h stack_internal.h
+SKIPHEADERS-$(CONFIG_VAAPI)                  += vaapi_vpp.h
 SKIPHEADERS-$(CONFIG_VULKAN)                 += vulkan.h vulkan_filter.h
 
 TOOLS     = graph2dot

libavfilter/stack_internal.h

@@ -19,12 +19,6 @@
 #ifndef AVFILTER_STACK_INTERNAL_H
 #define AVFILTER_STACK_INTERNAL_H
 
-#include <stdint.h>
-
-#include "libavutil/attributes.h"
-#include "framesync.h"
-#include "vaapi_vpp.h"
-
 enum {
     STACK_H = 0,
     STACK_V = 1,