Remove function singlesignon_perm() / code clean-up

The permissions in singlesignon_perm() are duplicates from the node and system module. You should not declare them again.

/**
 * Implementation of hook_perm().
 *
 * Defines permission names for this module.
 */
function singlesignon_perm() {
  return array('access content', 'access administration pages');
}

Thanks for this module! I have implemented it for a big Swedish client and it's working very well.