Deleting email address

Is that email address your Apple ID? If so, you can create a new email address and change your Apple ID to this new email by following the Support Article here. I would not recommend using an @iCloud email address as your Apple ID, because if you forget your Password you will not have any access to that email account to reset it if needed.

Change your Apple ID - Apple Support

If that email address was one that was automatically created for you with your current Apple ID, then you can create different alias email addresses to use instead of that one.

Add and manage email aliases for iCloud Mail on iCloud.com - Apple Support

You won't be able to delete it for good, you can just prevent it from showing on your devices or create up to 3 additional email aliases to use instead. It appears you have already shut off it in the iCloud Email setting of your devices, but won't be able to remove it at iCloud.com.

Set up iCloud Mail on all your devices - Apple Support