Remove documentation for functions removed from PHP (#135)

These 14 files document functions that have been removed from PHP and
whose EN documentation pages no longer exist:

- session_is_registered, session_register, session_unregister (removed in PHP 5.4)
- call_user_method, call_user_method_array (removed in PHP 7.0)
- utf8_encode, utf8_decode (removed in PHP 9.0)
- php_logo_guid, zend_logo_guid, main (removed in PHP 5.5)
- fgetwrapperdata (never released)
- debugger_off, debugger_on, define_syslog_variables (removed long ago)

Source: https://doc.php.net/revcheck.php?p=oldfiles&lang=it

Author: lacatoire