V4L/DVB (11391): pci-isa radios: remove open and release functions

Patch removes empty open and release functions in pci and isa radio
drivers, setting them to NULL. V4L module doesn't call for them due to
previous patch.

Signed-off-by: Alexey Klimov <klimov.linux@gmail.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab@redhat.com>