doc: remove old TODO

Removed

   # TODO: we need to delete documents when a property is *reindexed*

as add_text that does the reindexing uses replace_document that does
an upsert operation. The original TODO was added when add_document was
used to insert a document.

Author: rouilj

roundup/backends/indexer_xapian.py

@@ -9,8 +9,6 @@
 from roundup.backends.indexer_common import Indexer as IndexerBase
 from roundup.i18n import _
 
-# TODO: we need to delete documents when a property is *reindexed*
-
 # Note that Xapian always uses UTF-8 encoded string, see
 # https://xapian.org/docs/bindings/python3/introduction.html#strings:
 # "Where std::string is returned, it's always mapped to bytes in