Remove obsolete DOM function-style documentation (#133)

* Remove obsolete DOM function-style documentation

These 85 files use the old function-style format (dom/functions/).
The EN documentation has been restructured to use the OOP class format,
making these translations orphaned.

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

* Restore dom-import-simplexml.xml (still present in doc-en)

Author: lacatoire