* src/input/demux.c: skip header id3tag in the core before loading the demux (id3tags have a tendency to mess probing).
* modules/demux/flac.c, modules/demux/mpeg/m4a.c,mpga.c: update id3tag parsing.
* modules/demux/util/id3tag.c: id3tag parsing doesn't need to skip the id3tag header anymore.
* modules/demux/util/id3.c: module removed because id3tag header skipping isn't needed anymore.