[media] gspca - main: Remove USB traces

The USB traces are better done by usbmon which is enabled in most Linux/GNU
distributions and which permits easier comparison with the USB exchanges of
other drivers.

Signed-off-by: Jean-François Moine <moinejf@free.fr>
Signed-off-by: Mauro Carvalho Chehab <mchehab@redhat.com>