Follow-up to Clip negative atom densities: Cleanup of redundant warnings and clips

[yrrepy]

Description

What's this? Yes a PR that only removes lines of code.
Yay!

A sweep-up of lingering warning statements and positivity enforcement, prior to negative atom density clipping being moved closer to the CRAM solver by #3879

Because of the clip in abc.py

        # Clip unphysical negative number densities
        for r in results:
            r.clip(min=0.0, out=r)

These lingering else statements are no longer reachable.
They are redundant, in effect: dead code

[paulromano]

Ah yes, I love PRs that are all red! 🔪 Thanks for the cleanup @yrrepy!