Prevent unlinking of a Google skeleton profile

[rogerdahl]

Google skeleton profiles can't be upgraded to full because that would change the EDI-ID. Instead, we link those profiles. It doesn't make sense to unlink them because they can't be logged into separately once a full profile exists for the Google account, and because including permissions from the skeleton profile is almost certainly what the user would want. We should either explain what's going on when they click Unlink, or we should gray out the Unlink button and explain in a tooltip. We should not just hide the button.