remove dubious legal statment from uio-howto

UIO currently contains a rather dubious statement which wants removing.

The actual questions around whether user space code that depends tightly
on kernel GPL code designed to co-work with it are derivative works of
the kernel is extremely complex, and since we don't have space for either
a masters length essay on legal issues or need to start flamewars lets
simply remove the comment and leave law to lawyers

Signed-off-by: Alan Cox <alan@redhat.com>
Signed-off-by: Linus Torvalds <tovalds@linux-foundation.org>