Guess that Nom+Acc become Gen in negative, remove neggen field

This removes around 70k concrete categories (in PGFs compiled with
--optimize-pgf.)
Unsure if that is actually useful -- the number of concrete functions
only went down by a couple hundred.

src/russian/ParamRus.gf

@@ -105,7 +105,7 @@ oper
     -- refl : Reflexivity ;
     -- tran : Transitivity
     } ;
-  ComplementCase : Type = {s : Str ; c : Case ; neggen : Bool ; hasPrep : Bool} ;
+  ComplementCase : Type = {s : Str ; c : Case ; hasPrep : Bool} ;
   VerbForms2 : Type = VerbForms ** {c : ComplementCase} ;
   VerbForms3 : Type = VerbForms ** {c : ComplementCase ; c2 : ComplementCase} ;
 
@@ -115,4 +115,11 @@ oper
       <_,Transitive> => Trans ;
       <_,Intransitive> => Intrans
     } ;
+
+  -- Whether the noun that the preposition governs turns genitive in negative context
+  -- NB. I'm just guessing here, this is an exercise in shaving concrete categories. /IL
+  neggen : ComplementCase -> Bool = \c -> case c.c of {
+    Nom|Acc => True ;
+    _       => False
+    } ;
 }