Revert "Add warning on future breakage"

Did not really break but let's use upstream rather than local fixes
This reverts commit cbf67246e5.

book/tex4ebook.cfg

@@ -33,13 +33,4 @@
 }
 \makeatother
 
-% Warnig from Michal: Note that once you get the updated TeX Live with a new
-% `chemfig.4ht` file, you can remove this from the config file:
-%
-%```latex \pend:def\schemestart{\Picture+{}}
-%\append:def\CF_schemestop{\EndPicture} ```
-%
-%You could get an error otherwise, as there would be nested `\Picture+{}` and
-%`\EndPicture` commands.
-
 \EndPreamble