powerpc/ptrace: remove unused header includes

Remove unused header includes in ptrace.c and ptrace32.c

Signed-off-by: Christophe Leroy <christophe.leroy@c-s.fr>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Link: https://lore.kernel.org/r/6276df0be87a4329c2bb46b3b0f02059ae9e70e6.1582848567.git.christophe.leroy@c-s.fr