MIPS: Remove prototype for copy_user_page

MIPS architecture code does not provide copy_user_page,
so it should not provide a prototype for it either.

Signed-off-by: Guenter Roeck <linux@roeck-us.net>
Cc: linux-mips@linux-mips.org
Cc: linux-kernel@vger.kernel.org
Patchwork: https://patchwork.linux-mips.org/patch/9266/


Signed-off-by: Ralf Baechle <ralf@linux-mips.org>