Do not use Transformer for searchable text indexer

 Forcing the output to text/plain can lead to following Exception:
No transform path found from 'text/x-html-safe' to 'text/plain'. 

Leading to nothing being indexed for the specific tile that causes the error.

The catalog index takes care of the output we provide. Cleaning it up beforehand is not needed.
Ancient Plone (Products.Archetypes.BaseObject -> SearchAbleText) works similar.