powerpc/nohash: Remove DEBUG_HARDER

DEBUG_HARDER is not user selectable.

Remove it together with related messages.

Also remove two pr_devel() messages that should
likely have been pr_hard().

Signed-off-by: Christophe Leroy <christophe.leroy@csgroup.eu>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Link: https://lore.kernel.org/r/0f25109b0e12fdd1e6541dedbb2212cc53526a57.1622712515.git.christophe.leroy@csgroup.eu