This isn't actually a Lever setting, but a Google Calendar setting!
It's an account-level setting for your entire Google Apps Domain, meaning this must be changed by an administrator so feel free to share with someone on your team who has access to this page:.
Specifically at the following link:
There is an option as shown below:
Once you turn that off, you will no longer see Google Hangout links to your calendar invites unless you add them.