Revert "pc: memhp: force gaps between DIMM's GPA"

This reverts commit aa8580cddf011e8cedcf87f7a0fdea7549fc4704.

As described in
http://article.gmane.org/gmane.comp.emulators.qemu/371432
that commit causes linux guests to crash on memory hot-unplug.

The original problem it's trying to solve has now
been addressed within virtio.

Signed-off-by: Michael S. Tsirkin <mst@redhat.com>
