lavc: Remove old vaapi decode infrastructure

Deprecates struct vaapi_context and the installed header vaapi.h,
to be removed at the next version bump.

libavcodec/vaapi.h

@@ -32,6 +32,12 @@
 
 #include <stdint.h>
 
+#include "libavutil/attributes.h"
+
+#include "version.h"
+
+#if FF_API_VAAPI_CONTEXT
+
 /**
  * @defgroup lavc_codec_hwaccel_vaapi VA API Decoding
  * @ingroup lavc_codec_hwaccel
@@ -46,7 +52,10 @@
  * during initialization or through each AVCodecContext.get_buffer()
  * function call. In any case, they must be valid prior to calling
  * decoding functions.
+ *
+ * Deprecated: use AVCodecContext.hw_frames_ctx instead.
  */
+attribute_deprecated
 struct vaapi_context {
     /**
      * Window system dependent data
@@ -170,4 +179,6 @@ struct vaapi_context {
 
 /* @} */
 
+#endif /* FF_API_VAAPI_CONTEXT */
+
 #endif /* AVCODEC_VAAPI_H */