Don't install LaTeX module when installing the mathjax macro

The LaTeX module is only needed if the LaTeX exporter is used and thus shouldn't be installed by default. For now, the dep should be removed at https://github.com/xwiki-contrib/macro-mathjax/blob/master/macro-mathjax-ui/pom.xml#L46-L51

See also forum discussion to handle this better in the future by adding a new feature of EM.