MAINTAINERS: Remove myself as a KVM/arm64 reviewer

Haven't done any meaningful reviews for more than a year, and it doesn't
look like I'll be able to do so in the future. Make it official and remove
myself from the KVM/arm64 "Reviewers" list.

Signed-off-by: Alexandru Elisei <alexandru.elisei@arm.com>
Signed-off-by: Marc Zyngier <maz@kernel.org>
Link: https://lore.kernel.org/r/20230103120736.116523-1-alexandru.elisei@arm.com