How to delete a support community account

You can not delete your support community account. Just stop using it and it will fade into oblivion.

If your issue is with the many email messages about forum activity, then you can stop that through the forum preferences for your account: Your Profile & Preferences - Apple Community

In the section ‘Messages from Apple’, you may deselect the checkboxes that cause the flood of messages:

Hello~ It looks like you’re subscribed to the iPhone forum. If you go back and unsubscribe from that …it will greatly reduce your subscriptions if that’s an issue.

~Katana-San~