disable automatic Google Hangouts/Meet links, remove manual step

This removes the mention of a manual step to remove the automatic Google Hangouts/Meet link added by default for new Google Calendar events. Before merging this, a G Suite admin for gitlab.com should follow the steps at https://support.google.com/a/answer/6188027?hl=en.

We found this change helpful at Sourcegraph, so I thought I'd propose it here. Feel free to close/disregard. :)