Remove compat with old FFmpeg decoding API

The new API has been introduced in 2016 in libavcodec 57.xx, it's very
old.

This will avoid to maintain two code paths for decoding.

app/src/compat.h

@@ -8,7 +8,6 @@
 # define _DARWIN_C_SOURCE
 #endif
 
-#include <libavcodec/version.h>
 #include <libavformat/version.h>
 #include <SDL2/SDL_version.h>
 
@@ -33,15 +32,6 @@
 # define SCRCPY_LAVF_REQUIRES_REGISTER_ALL
 #endif
 
-// In ffmpeg/doc/APIchanges:
-// 2016-04-21 - 7fc329e - lavc 57.37.100 - avcodec.h
-//   Add a new audio/video encoding and decoding API with decoupled input
-//   and output -- avcodec_send_packet(), avcodec_receive_frame(),
-//   avcodec_send_frame() and avcodec_receive_packet().
-#if LIBAVCODEC_VERSION_INT >= AV_VERSION_INT(57, 37, 100)
-# define SCRCPY_LAVF_HAS_NEW_ENCODING_DECODING_API
-#endif
-
 #if SDL_VERSION_ATLEAST(2, 0, 5)
 // <https://wiki.libsdl.org/SDL_HINT_MOUSE_FOCUS_CLICKTHROUGH>
 # define SCRCPY_SDL_HAS_HINT_MOUSE_FOCUS_CLICKTHROUGH

app/src/decoder.c

@@ -36,9 +36,6 @@ decoder_close(struct decoder *decoder) {
 
 bool
 decoder_push(struct decoder *decoder, const AVPacket *packet) {
-// the new decoding/encoding API has been introduced by:
-// <http://git.videolan.org/?p=ffmpeg.git;a=commitdiff;h=7fc329e2dd6226dfecaa4a1d7adf353bf2773726>
-#ifdef SCRCPY_LAVF_HAS_NEW_ENCODING_DECODING_API
     int ret;
     if ((ret = avcodec_send_packet(decoder->codec_ctx, packet)) < 0) {
         LOGE("Could not send video packet: %d", ret);
@@ -53,19 +50,5 @@ decoder_push(struct decoder *decoder, const AVPacket *packet) {
         LOGE("Could not receive video frame: %d", ret);
         return false;
     }
-#else
-    int got_picture;
-    int len = avcodec_decode_video2(decoder->codec_ctx,
-                                    decoder->video_buffer->producer_frame,
-                                    &got_picture,
-                                    packet);
-    if (len < 0) {
-        LOGE("Could not decode video packet: %d", len);
-        return false;
-    }
-    if (got_picture) {
-        video_buffer_producer_offer_frame(decoder->video_buffer);
-    }
-#endif
     return true;
 }