Remove superfluous RP argument to EmptyRelSlash.

next-lib/src/english/ExtraEng.gf

@@ -10,7 +10,7 @@ concrete ExtraEng of ExtraEngAbs = CatEng **
         rp.s ! RC (fromAgr ag).g Acc ++ slash.s ! t ! a ! p ! ODir ++ slash.c2 ;
       c = Acc
       } ;
-    EmptyRelSlash rp slash = {
+    EmptyRelSlash slash = {
       s = \\t,a,p,_ => slash.s ! t ! a ! p ! ODir ++ slash.c2 ;
       c = Acc
       } ;