[media] DocBook/dvbproperty.xml: Fix ISDB-T delivery system parameters

The ISDB-T differs on its way to implement the hierarchical
transmissions: instead of using a low-priority/high-priority
FEC codes, it does that by using different layers, each layer
with their groups of segments. So, those parameters don't make sense
for ISDB-T.

Signed-off-by: Mauro Carvalho Chehab <mchehab@redhat.com>