libxml2 and deprecated API calls

[Greg Troxel <gdt%lexort.com@localhost>]

It looks like libxml2 does not enable deprecated APIs and thus
xmlCleanupPredefinedEntities is not available.
However py-libxml2 seems to want to use it.  This results in (on macOS):

  $ echo 'import libxml2' | python3.11
  Traceback (most recent call last):
    File "<stdin>", line 1, in <module>
    File "/opt/pkg/lib/python3.11/site-packages/libxml2.py", line 1, in <module>
      import libxml2mod
  ImportError: dlopen(/opt/pkg/lib/python3.11/site-packages/libxml2mod.so, 2): Symbol not found: _xmlCleanupPredefinedEntities
    Referenced from: /opt/pkg/lib/python3.11/site-packages/libxml2mod.so
    Expected in: flat namespace
   in /opt/pkg/lib/python3.11/site-packages/libxml2mod.so

I haven't tried other systems yet, but I wonder if anyone else is seeing
this.

(pkgsrc head, up to date)