header guards: clean up some stragglers

Some headers had been missed during the initial header guard
standardization.

Signed-off-by: Cornelia Huck <cohuck@redhat.com>
Reviewed-by: Laurent Vivier <lvivier@redhat.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
Message-Id: <20210610135937.94375-2-cohuck@redhat.com>