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It became a bit distracting.

This replaces the use of `variable-pitch-mode`, which prevented fixed
pitch for, e.g., code blocks.

The ucs-utils package makes Emacs shutdown much slower and back-button
can work just fine without it.

This fixes a few build warnings concerning undefined variables.

In particular, rely on some defaults set in the emacs init module.

Unfortunately, a few sites go nuts if they don't get the path.

Also remove nixos-19.09-small.

Wasn't as much fun as I had hoped.

Instead enable them in individual configurations where they are used.