doc-rst: remove an invalid include from the docs

I suspect that this is a left over from Markus tests.
Signed-off-by: Mauro Carvalho Chehab <mchehab@s-opensource.com>

Documentation/linux_tv/media/dvb/audio_h.rst

@@ -7,5 +7,3 @@ DVB Audio Header File
 *********************
 
 .. kernel-include:: $BUILDDIR/audio.h.rst
-
-.. kernel-include:: $BUILDDIR/../../../../etc/adduser.conf