MNT: Remove setting of mathjax CDN
MNT: Remove setting of mathjax CDN

Sphinx does this correctly now.

ahaberlie/MetPy,jrleeman/MetPy,jrleeman/MetPy,dopplershift/MetPy,ahaberlie/MetPy,Unidata/MetPy,Unidata/MetPy,dopplershift/MetPy,ShawnMurd/MetPy