Make internal Matroska demuxer default again

Undo Aurelien's previous commit which made the lavf demuxer the
default. SSA/ASS subtitles do not work properly with the lavf demuxer
at the moment. That's much more important than any issues with the
internal demuxer. The internal demuxer must remain the default at least
until the subtitle issues are resolved.

git-svn-id: svn://svn.mplayerhq.hu/mplayer/trunk@27556 b3059339-0415-0410-9bf9-f77b7e298cf2

libmpdemux/demux_lavf.c

@@ -183,7 +183,6 @@ static const char *preferred_list[] = {
     "mov,mp4,m4a,3gp,3g2,mj2",
     "mpc",
     "mpc8",
-    "matroska",
     NULL
 };