Remove alpha kernel code to process userland misaligned accesses, and the

Remove alpha kernel code to process userland misaligned accesses, and the
machdep.unaligned_* sysctl to control its behaviour. Such code made sense more
than 20 years ago where a lot of code was not 64-bit clean, but this is no
longer the case those days.

ok jsg@ millert@ deraadt@