.htaccess: Remove `php_flag register_globals Off`

The `register_globals` directive is not required anymore as it
defaults to `off` starting with PHP 4.2.0, is deprecated as of
PHP 5.3.0 and removed as of PHP 5.4.0:
http://www.php.net/manual/en/ini.core.php#ini.register-globals

Also, support for PHP 4 has been discontinued since 2007-12-31:
http://php.net/releases/index.php