V4L/DVB (3386): Dvb-core: remove dead code

The field "dvr" in struct dmxdev is competely unused. Remove
it and code which allocates, initializes and frees it.

Signed-off-by: Peter Beutner <p.beutner@gmx.net>
Signed-off-by: Johannes Stezenbach <js@linuxtv.org>
Signed-off-by: Mauro Carvalho Chehab <mchehab@infradead.org>