MAINTAINERS: powerpc: Remove Aneesh

Aneesh is stepping down from powerpc maintenance.

Acked-by: Aneesh Kumar K.V (Arm) <aneesh.kumar@kernel.org>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Link: https://msgid.link/20240430044228.49015-1-mpe@ellerman.id.au