disables Google Analytics on docs site (#1113)

This is a follow-up from a private maintainer discussion (https://github.com/orgs/just-the-docs/teams/maintainers/discussions/11?from_comment=12). The cliff's notes for the public are: we believe we are not currently GDPR-compliant in how the docs site itself serves analytics.

For now, we'll disable analytics; we don't use them anyways. We will then:

- add analytics and the relevant banner to the regression test repository
- in the future, workshop a built-in solution for JtD users to be GDPR compliant
- optionally, clarify the role of users of this theme (their responsibility is to make their sites GDPR compliant)(

_config.yml

@@ -151,8 +151,9 @@ callouts:
 
 # Google Analytics Tracking (optional)
 # Supports a CSV of tracking ID strings (eg. "UA-1234567-89,G-1AB234CDE5")
-ga_tracking: UA-2709176-10,G-5FG1HLH3XQ
-ga_tracking_anonymize_ip: true # Use GDPR compliant Google Analytics settings (true/nil by default)
+# Note: the main Just the Docs site does *not* use Google Analytics.
+# ga_tracking: UA-2709176-10,G-5FG1HLH3XQ
+# ga_tracking_anonymize_ip: true # Use GDPR compliant Google Analytics settings (true/nil by default)
 
 plugins:
   - jekyll-seo-tag