how to unlocalize theme/plugin?

The main problem is that you removed the sprintf.

Replace the echo with sprintf and remove the ().

Should be like this

'logged_in_as' => '<p class="logged-in-as">'.
                    sprintf( 'Logged in as <a href="%1$s">%2$s</a>. <a href="%3$s" title="Log out of this account">Log out?</a>',
                    admin_url( 'profile.php' ),
                    $user_identity,
                    wp_logout_url( apply_filters( 'the_permalink', get_permalink( ) ) ) ).
                  '</p>',

Be careful! changing code directly in a plugin will lead to problems.

Next plugin update your code will be removed so be mindful.

If you can try using a filter, if the plugin has one. That way the changed you are doing when connecting to that filter will stay, unless the plugin author changed the filter name =]