Fix -Wunused-but-set-global warnings - #25245

I was slightly confused why the php_token_ce is unused, the reason is that PHP_METHOD(PhpToken, tokenize) gets the token class via: token_class = zend_get_called_scope(execute_data); which may seems odd at first, but it's to allow the class to be extended and creates instances of the subclass. (Which probably should have a comment to explain it).

The zend_test are quite obviously correct.

For the user_filter_class_entry it currently makes sense as it is only ever used as an "implicit" requirement to be extended, but I've thought that maybe we should require that registering a userland filter extends from it. But then the API is very clunky (defining onCreate/onClose methods rather than using normal constructor/destructor) so maybe creating a new interface would just be better.