stream: get rid of streamtype enum

Because it's kind of dumb. (But not sure if it was worth the trouble.)

For stream_file.c, we add new explicit fields. The rest are rather
special uses and can be killed by comparing the stream impl. name.

The changes to DVD/BD/CD/TV are entirely untested.

stream/stream_cdda.c

@@ -383,7 +383,6 @@ static int open_cdda(stream_t *st)
 
     st->streaming = true;
 
-    st->type = STREAMTYPE_CDDA;
     st->demuxer = "+disc";
 
     print_cdtext(st, 0);