avcodec: add a Vorbis parser to get packet duration

This also allows for removing some of the Vorbis-related hacks.

libavcodec/allcodecs.c

@@ -416,6 +416,7 @@ void avcodec_register_all(void)
     REGISTER_PARSER  (RV30, rv30);
     REGISTER_PARSER  (RV40, rv40);
     REGISTER_PARSER  (VC1, vc1);
+    REGISTER_PARSER  (VORBIS, vorbis);
     REGISTER_PARSER  (VP3, vp3);
     REGISTER_PARSER  (VP8, vp8);