[media] pvrusb2: Get rid of obsolete code for video standard enumeration

Get rid of pvrusb2-local implementation for enumeration of video
standards - with video_ioctl2 this happens automatically now in the
v4l core.

Signed-off-by: Mike Isely <isely@pobox.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab@redhat.com>