The registration or create account portlet in Liferay portal can be customized to add/remove some of its field without any coding.
This blog explain some of these customization properties which developers can add them in portal-ext to change the behavior of user registration portlet.
users.screen.name.always.autogenerate - If you do not want your users to provide screen name, you can use this property hide screen name text field. The default value is false. If it is changed to true, the screen name field will not appear on the registration page and screen name will be auto generated by the portal.
login.create.account.allow.custom.password - The default registration portlet in Liferay doesn't provide option of password selection to user. If this property is set to true, the registration screen will show password fields to user and user can provide password of his/her choice.
field.enable.com.liferay.portal.model.Contact.male - If your site is not interested in knowing the gender of the user, you can remove gender selection from the page by setting false value of this property.
field.enable.com.liferay.portal.model.Contact.birthday - Last configuration is for birth date field. You can remove bith date selection by setting false value to this property.
captcha.check.portal.create_account - This propery can be used to tell whether or not to use captcha checks for the account creation.
users.email.address.required - Set this to false if you want to be able to create users without an email address. An email address will be automatically assigned to a user based on the property "users.email.address.auto.suffix". If user is entering his email id, the system will not generate a new one. Usually, setting this property to false will make sense when you don't want user to use email address for login.