remove old LaTeX xslt file

hasn't been used ever!
All displayed text is localised

Text written in the XSLT files and index.html is now run through the localiser, which reads strings from scripts/R/en-gb.js

In XSLT files, the <localise>key</localise> tag is replaced with R(key).
In index.html, tags with the attribute data-localise="key" have their contents set to R(key).
add command-line option to choose language

-l, or --locale, specifies which language file to use. Default is en-GB.

New language files should go in the `locales` folder.