Removed \newcommand lines at the end of .md files

[jiegillet]

They were not necessary. I left them in math.md, but I can remove them from there too if necessary.

For future reference, because I spent WAY too much time on this than I wish to admit, here is the command I used:

find contents -name "*.md" | xargs -I {} sh -c "sed -i.bkp "'"1,/<\/script>/ !d"'" {}"

[june128]

I checked the chapters and removing this doesn't seem to affect the LaTeX.