Revert "spapr: fix memory hot-unplugging"

This reverts commit fe6824d1.

Conflicts hw/ppc/spapr_drc.c, because get_index() has been renamed
spapr_get_index().

This didn't fix the problem. Once the hotplug has been started
some memory is allocated and some structures are allocated.
We don't free it when we ignore the unplug, and we can't because
they can be in use by the kernel.

Signed-off-by: Laurent Vivier <lvivier@redhat.com>
Tested-by: Daniel Barboza <danielhb@linux.vnet.ibm.com>
Signed-off-by: David Gibson <david@gibson.dropbear.id.au>