powerpc/64e: Remove unused REGION related macros

Those macros are not used anywhere. Remove them as they are soon
going to be wrong and are not worth modifying as they are not used.

Signed-off-by: Christophe Leroy <christophe.leroy@csgroup.eu>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Link: https://lore.kernel.org/r/f0efde8cee0924c3991790042b176ac77ad35e1f.1656427701.git.christophe.leroy@csgroup.eu