Clarify deprecation of ElementTree.XMLParser(html=...) parameter

Lib/xml/etree/ElementTree.py

@@ -1454,7 +1454,7 @@ class TreeBuilder:
 class XMLParser:
     """Element structure builder for XML source data based on the expat parser.
 
-    *html* are predefined HTML entities (not supported currently),
+    *html* are predefined HTML entities (deprecated and not supported),
     *target* is an optional target object which defaults to an instance of the
     standard TreeBuilder class, *encoding* is an optional encoding string
     which if given, overrides the encoding specified in the XML file: