Update, minibufexpl.txt: removed the colorcolum--`cc=79`--specification ...

...from the modeline.  It's super unsightly and annoying.

If it's used to help keep things lined up while adding to the docs, then I'd recommend only using `cc=79` on a separate branch from master, making sure that you always remove the `cc=79` from master's copy of the docs after each merge.