V4L/DVB (6694): pvrusb2: Remove obsolete global hardware type enumeration

Device-specific driver behavior is now defined by generic device
characteristics rather than by specific device model information.
With this change, the hardware type field can go away, thus this
change.

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