powerpc/powernv: Remove unused definitions in opal-api.h

This removes definitions in opal-api.h that are completely unused in
Linux.

For each of these I see three possibilities, 1) we *should* be using
them in Linux and patches will arrive to do that, 2) they are not used
but should stay in the header to document the API for some important
reason, 3) they are not used and needn't be part of the API.

Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Reviewed-by: Stewart Smith <stewart@linux.vnet.ibm.com>