staging: xgifb: delete support for Chrontel 7017 TV output

IF_DEF_CH7017 is hard-coded to 0, so this is all just dead code that
can be deleted.

Signed-off-by: Aaro Koskinen <aaro.koskinen@iki.fi>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>