powerpc/kuap: Remove KUAP_CURRENT_XXX

book3s/32 was the only user of KUAP_CURRENT_XXX.

After rework of book3s/32 KUAP, it is not used anymore.

Remove them.

Signed-off-by: Christophe Leroy <christophe.leroy@csgroup.eu>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Link: https://lore.kernel.org/r/549214ecf6887d965645e664520d4886663c5ffb.1622708530.git.christophe.leroy@csgroup.eu