[tex-eplain] Workaround/fix for recent color breakage.

[David Koppelman]

As reported by others, the LaTeX color package no longer works with
eplain. It worked for me in TeX Live 2021 but it is not working in TeX
Live 2022. The problem is due to the color.sty file including
mathcolor.ltx.

For those experiencing the problem there is an easy workaround: Put
the following line before your "\input eplain" line in your TeX source
file:

 \def\mathcolor{}

Or, you could put a copy of
/usr/local/texlive/2022/texmf-dist/tex/eplain/eplain.tex in your own
TeX input directory (if you have one) and then add \def\mathcolor{}
near the top of the file.

Of course, it is up to the eplain or maybe color.sty maintainer to
apply a proper fix.

David