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/bulgarian/LangBul.gf

@@ -3,8 +3,8 @@
 concrete LangBul of Lang = 
   GrammarBul,
   LexiconBul,
-  ConstructionBul,
-  DocumentationBul
+  ConstructionBul
+  ,DocumentationBul --# notpresent
   ** {
 
 flags startcat = Phr ;