MDL-77338 backup: Added class properties that are not declared.

In PHP 8.2 and later, setting a value to an undeclared class property is
deprecated and emits a deprecation notice.
So we need to add missing class properties that still need to be declared.

backup/util/xml/parser/progressive_parser.class.php

@@ -85,7 +85,6 @@ class progressive_parser {
 
         $this->file     = null;
         $this->contents = null;
-        $this->procesor = null;
         $this->level    = 0;
         $this->path     = '';
         $this->accum    = '';