New_user_approve_$Status_user
Perform An Action When A User’s Status Is Updated To A Specific Action.
$Status Will Be Either Approve Or Deny.
function deny_user( $user_id ) {
wp_delete_user( $user_id );
}
add_action( 'new_user_approve_deny_user', 'deny_user' );
See Also: New_user_approve_user_status_update