Update Google Analytics tracker config

Removes the following fields from the tracker
config:
- `name`, which was erroring due to it
  including a `.`
- `displayFeaturesTask` which seems to be
  deprecated

Also refactors the `create` command to put all
fields into the options parameter, as shown in the
developer docs:

https://developers.google.com/analytics/devguides/collection/analyticsjs/creating-trackers

app/assets/javascripts/analytics/init.js

@@ -24,9 +24,8 @@
         trackingId: trackingId,
         cookieDomain: 'auto',
         anonymizeIp: true,
-        displayFeaturesTask: null,
+        allowAdFeatures: false,
         transport: 'beacon',
-        name: 'GOVUK.analytics',
         expires: 365
       });