Remove comment from _Wikitext_append_entity_from_utf32_char

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.

Signed-off-by: Wincent Colaiuta <win@wincent.com>