MAINTAINERS: remove Aurelien and David from matroska*

Aurelien last activity in git is from 2017, last activity on the ML is from 2018
David last activity in git is from 2011, and ML from 2013

matroska* is actively maintained

CC: Aurelien Jacobs <aurel@gnuage.org>
CC: David Conrad <lessen42@gmail.com>
Signed-off-by: Michael Niedermayer <michael@niedermayer.cc>

MAINTAINERS

@@ -416,9 +416,9 @@ Muxers/Demuxers:
   libopenmpt.c                          Josh de Kock
   lmlm4.c                               Ivo van Poorten
   lxfdec.c                              Tomas Härdin
-  matroska.c                            Aurelien Jacobs, Andreas Rheinhardt
-  matroskadec.c                         Aurelien Jacobs, Andreas Rheinhardt
-  matroskaenc.c                         David Conrad, Andreas Rheinhardt
+  matroska.c                            Andreas Rheinhardt
+  matroskadec.c                         Andreas Rheinhardt
+  matroskaenc.c                         Andreas Rheinhardt
   matroska subtitles (matroskaenc.c)    John Peebles
   metadata*                             Aurelien Jacobs
   microdvd*                             Aurelien Jacobs