sparc: Kill user copy check code.

For whatever reason GCC isn't able to figure things out in
the control flow (in particular when min() and max() expressions
are involved) on sparc as well as it can on x86.

So lots of useless incorrect user copy warnings get spewed and the
full-on compile failure mode of the user copy checks were never usable
on sparc at all.

People can debug these kinds of problems on x86.

Signed-off-by: David S. Miller <davem@davemloft.net>