powerpc: Remove the celleb support

The celleb code has seen no actual development for ~7 years.

We (maintainers) have no access to test hardware, and it is highly
likely the code has bit-rotted.

As far as we're aware the hardware was never widely available, and is
certainly no longer available, and no one on the list has shown any
interest in it over the years.

So remove it. If anyone has one and cares please speak up.

Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Acked-by: Benjamin Herrenschmidt <benh@kernel.crashing.org>
Acked-by: Jeremy Kerr <jk@ozlabs.org>

arch/powerpc/include/asm/smp.h

@@ -125,7 +125,6 @@ extern irqreturn_t smp_ipi_demux(void);
 
 void smp_init_pSeries(void);
 void smp_init_cell(void);
-void smp_init_celleb(void);
 void smp_setup_cpu_maps(void);
 
 extern int __cpu_disable(void);