Completely revert r334707.

This removes a since-completed TODO item and reinstates the newer wording for
the default_charset paragraph, which includes a complete list of affected
functions and is therefore hopefully better than the suggested text.


git-svn-id: https://svn.php.net/repository/phpdoc/en/trunk@334740 c90b9560-bf6c-de11-be94-00142212c4b1