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.

lib/src/italian/LangIta.gf

@@ -3,7 +3,7 @@
 concrete LangIta of Lang = 
   GrammarIta,
   LexiconIta
-  ,DocumentationIta
+  ,DocumentationIta --# notpresent
   ,ConstructionIta
   ** {