Remove INN/Largo Project Google Analytics tracking from Largo.

[benlk]

Changes

• removes the Google Analytics tracking of INN Members
• removes the Google Analytics tracking of all Largo users
• changes the logic within largo_google_analytics() so that Google Analytics is only loaded if the site has configured a Google Analytics ID in the Largo theme options.
• minor code cleanup within largo_google_analytics()

Why

Well, for starters, privacy and as part of #1495 "what do we need to do for WordPress 4.9.6 and the GDPR?" question. And also because removing GA increases page speed.

But also because this always-on Google Analytics sometimes conflicts with other Google Analytics tags. It's an older tag, and it doesn't check out.

This solution shouldn't conflict with INN/umbrella-rivard-report#30 or similar child theme changes that remove_action( 'wp_head', 'largo_google_analytics' );.

Questions

• is that of_get_option() comparison safe?
• does this need docs for anything? Is it just something that we'll just add to the changelog?
• are there tests that are affected?

post-merge todo:

• add to changelog
• figure out how we're going to request/acquire lists of Largo-using sites in the future.

[benlk]

figure out how we're going to request/acquire lists of Largo-using sites in the future.

That continues in #1495.