Makefile.inc1: Remove non-NO_ROOT cases from distributeworld

As of commit 41adc5f29ba6 ("release: Always use NO_ROOT for distribute*
and package*") we pass -NO_ROOT for the release image artifact build
targets. For distributeworld, add a check that NO_ROOT and METALOG are
set, and then remove tests for them being set.

This is an incremental step towards the goal of having all targets in
release/Makefile run without requiring root.

Reviewed by: brooks
Sponsored by: The FreeBSD Foundation
Differential Revision: https://reviews.freebsd.org/D48095