[PATCH] powerpc: remove redundant code in stab init

There's never been a hardware platform that has both pSeries/RPA LPAR
hypervisor and stab (pre-POWER4 segment management). This removes
the redundant code in stab_initalize().

Signed-off-by: Olof Johansson <olof@lixom.net>
Signed-off-by: Paul Mackerras <paulus@samba.org>