devel/renpy6: unbreak with ffmpeg 4.0

ffdecode.c:840:67: error: use of undeclared identifier 'CODEC_CAP_DELAY'

if (!pkt_temp->data && dec->codec->capabilities & CODEC_CAP_DELAY)
                                                  ^

ffdecode.c:1246:29: error: use of undeclared identifier 'CODEC_FLAG2_FAST'

if(fast) enc->flags2 |= CODEC_FLAG2_FAST;
                        ^

PR: 227726