Fixed a bug in the datacon names extension in the dynamic linker

My code was doing unnecessary work when trying to get hold of all the BCOs in order to sniff the datacon names.
This involved calculating the transitive closure of a relation and was causing a huge performance slowdown in GHCi, as benchmarks uncovered. It turns out that this calculation was unnecessary.

compiler/ghci/Linker.lhs

@@ -750,22 +750,14 @@ linkSomeBCOs toplevs_only ie ce_in de_in ul_bcos
 		     -- closure environment, which leads to trouble.
 		     ASSERT (all (not . (`elemNameEnv` ce_in)) (map fst ce_additions))
 		     extendClosureEnv ce_in ce_additions
-            refs  = goForRefs ul_bcos
-            names = nub$ concatMap (ssElts . unlinkedBCOItbls) (ul_bcos ++ refs)
+            names = concatMap (ssElts . unlinkedBCOItbls) ul_bcos
         addresses <- mapM (lookupIE ie) names
         let de_additions = [(address, name) | (address, name) <- zip addresses names
                                             , not(address `elemAddressEnv` de_in) 
                            ]
             de_out = extendAddressEnvList de_in de_additions
         return ( ce_out, de_out, hvals)
-    where 
-          goForRefs = getRefs []
-          getRefs acc []  = acc
-          getRefs acc new = getRefs (new++acc) 
-                 [bco | BCOPtrBCO bco <- concatMap (ssElts . unlinkedBCOPtrs) new
-                      , notElemBy bco (new ++ acc) nameEq]
-          ul1 `nameEq` ul2 = unlinkedBCOName ul1 == unlinkedBCOName ul2
-          (x1 `notElemBy` x2) eq = null$ intersectBy eq [x1] x2
+
 \end{code}