powerpc: Remove stubbed beat smp support

I have no idea if the beat hypervisor supports multiple cpus in
a partition, but the code has not been touched since these stubs
were added in February of 2007 except to move them in April of 2008.
These are stubs: start_cpu always returns fail (which is dropped),
the message passing and reciving are empty functions, and the top
of file comment says "Incomplete".

Signed-off-by: Milton Miller <miltonm@bga.com>
Signed-off-by: Benjamin Herrenschmidt <benh@kernel.crashing.org>