Remove getConstantFwdRef function

This function is unused and, as noted in
#266 (comment),
is almost certainly incorrect.

src/Data/LLVM/BitCode/IR/Values.hs

@@ -2,7 +2,7 @@
 
 module Data.LLVM.BitCode.IR.Values (
     getValueTypePair
-  , getConstantFwdRef, getConstantFwdRefAdjustedId
+  , getConstantFwdRefAdjustedId
   , getValue
   , getFnValueById, getFnValueById'
   , parseValueSymbolTableBlock
@@ -19,11 +19,6 @@ import Control.Monad ((<=<),foldM)
 
 -- Value Table -----------------------------------------------------------------
 
--- | Return a forward reference if the value is not in the incremental table.
-getConstantFwdRef :: ValueTable -> Type -> Int -> Parse (Typed PValue)
-getConstantFwdRef t ty n = label "getConstantFwdRef" $
-    adjustId n >>= getConstantFwdRefAdjustedId t ty
-
 getConstantFwdRefAdjustedId :: ValueTable -> Type -> Int -> Parse (Typed PValue)
 getConstantFwdRefAdjustedId t ty n' = label "getConstantFwdRefAdjustedId" $ do
   mb <- lookupValue n'