KVM: powerpc: Remove AGGRESSIVE_DEC

Because we now emulate the DEC interrupt according to real life behavior,
there's no need to keep the AGGRESSIVE_DEC hack around.

Let's just remove it.

Signed-off-by: Alexander Graf <agraf@suse.de>
Acked-by: Acked-by: Hollis Blanchard <hollis@penguinppc.org>
Signed-off-by: Avi Kivity <avi@redhat.com>