I’d set a monthly reminder to check on this enhancement, and noticed the change last night. When clicking the user’s email to edit, the option appeared to the right to ‘Delete’ the primary email. In all of my updates last night, it worked as designed, and I no longer have an invalid None.com company or email domain. 
If you’re not seeing the same, HubSpot may be rolling this enhancement out in groups so hopefully a short wait should provide my same results for your team.
Delete primary email