[media] dtv-core: get rid of duplicated kernel-doc include

Somehow, two DVB headers were included twice. Remove the
duplication
Reported-by: NMarkus Heiser <markus.heiser@darmarit.de>
Signed-off-by: NMauro Carvalho Chehab <mchehab@s-opensource.com>

Documentation/media/kapi/dtv-core.rst

@@ -8,14 +8,6 @@ Digital TV Common functions
 
 .. kernel-doc:: drivers/media/dvb-core/dvbdev.h
 
-
-
-.. kernel-doc:: drivers/media/dvb-core/dvb_math.h
-   :export: drivers/media/dvb-core/dvb_math.c
-
-.. kernel-doc:: drivers/media/dvb-core/dvbdev.h
-   :export: drivers/media/dvb-core/dvbdev.c
-
 Digital TV Ring buffer
 ----------------------