All you need to do is Install and activate the Disable New User Notification Emails plugin. Upon activation, the plugin simply disables new user notification emails in WordPress. It works out of the box, and there are no settings for you to configure.
Please be cautious because it is out of date. Use at your own risk. I was getting so many emails because several of my sites where getting spammed. I used this and it helped.
This plugin disables new user notification emails in WordPress. That is all.
This plugin was created by Thomas Griffin.