Update the GA template usage section

Mostly to remove the async example (not relevant for GA4 which people should be using by now).

See https://github.com/gohugoio/hugo/issues/9987

content/en/templates/internal.md

@@ -45,20 +45,13 @@ googleAnalytics = "G-MEASUREMENT_ID"
 
 ### Use the Google Analytics Template
 
-You can then include the Google Analytics internal template:
+You can then include the Google Analytics internal template in the `<head>` section of your template:
 
-```
+```go-html-template
-{{ template "_internal/google_analytics.html" . }}
+{{ if hugo.IsProduction }}
-```
+    {{ template "_internal/google_analytics.html" . }}
-
+{{ end }}
-
+ ```
-```
-{{ template "_internal/google_analytics_async.html" . }}
-```
-
-When using Google Analytics v4 use `_internal/google_analytics.html`.
-
-A `.Site.GoogleAnalytics` variable is also exposed from the config.
 
 ## Disqus