Remove custom signup fields setting

[joshcanhelp]

Changes

Remove database-stored extra signup fields setting for the embedded login form. Custom fields must now be added by enqueueing a JS file before the embedded form loads:

function namespace_login_enqueue_scripts() {
        // This example assumes that this file is loaded from your theme.
	wp_enqueue_script( 'lock-signup-fields', get_stylesheet_directory_uri() . '/assets/js/lock-signup-fields.js' );
}
add_action( 'login_enqueue_scripts', 'namespace_login_enqueue_scripts' );

... that defines a specific global variable wpAuth0LockGlobalFields with the signup fields defined:

// lock-signup-fields.js
var wpAuth0LockGlobalFields = [
  {
    name: "full_name",
    placeholder: "your full name",
    validator: function(address) {
      return {
        valid: address.length >= 10,
        hint: "Must have 10 or more chars" // optional
      };
    }
  }
];

Checklist

• All existing and new tests complete without errors
• All code quality tools/guidelines in the Contribution guide have been run/followed
• All active GitHub CI checks have passed