Remove code which tries to get version information from darcs folder

gf.cabal

@@ -39,10 +39,6 @@ data-files:
   www/translator/*.css
   www/translator/*.js
 
---source-repository head
---  type:     darcs
---  location: http://www.grammaticalframework.org/
-
 source-repository head
   type:     git
   location: https://github.com/GrammaticalFramework/GF.git
@@ -162,7 +158,6 @@ Library
 
     GF.Data.Operations GF.Infra.Option GF.Infra.UseIO
 
-    DarcsVersion_gf
     GF.Command.Abstract
     GF.Command.CommandInfo
     GF.Command.Commands