remove email field from registration form
Mean that you can set an account without e-mail, as admin or someone that have rights, in url '/admin/people/create'. But when a visitor goes to 'user/register', he must specify a e-mail, because someday an e-mail will only be used if you wish to receive a new password, as description says.

There are two types of accounts, one with e-mail (like a visitor that created a new account), and another without e-mail (admin created a new user). This is why AccountForm check if user have an e-mail and check if user is admin or have 'users' permission, to set e-mail field required or not.

There is no reason to a visitor create a account without an e-mail, there is no other way to admin/system contact him for any kind of situation. In other hand if an admin create a new user, somehow he will able to contact the new user.