ppc: Remove stub of PPC970 HID4 implementation

ppc: Remove stub of PPC970 HID4 implementation

The PowerPC 970 CPU was a cut-down POWER4, which had hypervisor capability.
However, it can be (and often was) strapped into "Apple mode", where the
hypervisor capabilities were disabled (essentially putting it always in
hypervisor mode).

That's actually the only mode of the 970 we support in qemu, and we're
unlikely to change that any time soon.  However, we do have a partial
implementation of the 970's HID4 register which affects things only
relevant for hypervisor mode.

That stub is also really ugly, since it attempts to duplicate the effects
of HID4 by re-encoding it into the LPCR register used in newer CPUs, but
in a really confusing way.

Just get rid of it.

Signed-off-by: David Gibson <david@gibson.dropbear.id.au>
Reviewed-by: Cédric Le Goater <clg@kaod.org>
Reviewed-by: Greg Kurz <groug@kaod.org>