Remove openpyxl dependency

openpyxl, a package to use Excel files, was added nearly three years ago for Himanis folios in 6096eedf. This also pulls jdcal and et_xmlfile, and we do not use either of those three dependencies at all.

I noticed this while looking at !980 (closed) and !997 (closed), bumping both jdcal and openpyxl.