[v2] Don't add \text to operators whose name already include it. (#2222)

This PR prevents Mathjax from inserting another \text{} into an operator name that already has \text{} in it. It is not perfect, in that this does allow - and * to be rendered as mathematics in cases where LaTeX doesn't (e.g., \operatorname{\text{a}-\text{b}}), but is probably good enough for MathJax.

Resolves issue #2222 (closed).