Remove Google Analytics from the site pages

[martindholmes]

In this issue on the TEI repo:
TEIC/TEI#2748
Council agreed to remove the injected Google JS code from all pages on the site. I've made a change in tei-install.sh in the TEI repository, but I notice that the same code is injected into the non-Guidelines web pages, so the same change will have to be made in this repo (or whatever mechanism deploys the site pages). Then we can add a disclaimer page to the site as described in the other issue discussion.

[martindholmes]

I believe this could be achieved simply by deleting src/_includes/analytics.html and src/_includes/analytics.html_src. When I have time, I'll try this and check the results; in the meantime, anyone who understands this better than me could help by letting me know if there's anything else that would need to be done.