Lang???.gf: exclude Documentation from present mode

The Documentation module is excluded from present mode in abstract/Lang.gf,
so it needs to be excluded in the corresponding concrete syntaxes too
to avoid problems.

src/chinese/LangChi.gf

@@ -5,7 +5,7 @@ concrete LangChi of Lang =
   GrammarChi,
   LexiconChi
   ,ConstructionChi
-  ,DocumentationChi
+  ,DocumentationChi --# notpresent
   ** {
 
 flags startcat = Phr ; unlexer = concat ; lexer = text ;