Remove comment from _Wikitext_append_entity_from_utf32_char
There is no point in special casing entities like "quot", "amp"
and such in this function because neither of the two call sites
would ever pass in such a code point:
- the _Wikitext_append_sanitized_link_target already explicitly
handles all these cases, either emitting the entities manually
or raising an exception.
- the DEFAULT case won't ever have to process those characters
because they would have already been tokenized otherwise and
handled in the QUOT, AMP, LESS and GREATER cases.