Don't show the loaded packages in ":show packages"; fixes #4300

It's never worked properly, and the information is in ":show linker".

ghc/InteractiveUI.hs

@@ -1645,11 +1645,6 @@ showPackages = do
   io $ putStrLn $ showSDoc $ vcat $
     text ("active package flags:"++if null pkg_flags then " none" else "")
     : map showFlag pkg_flags
-  pkg_ids <- fmap (preloadPackages . pkgState) getDynFlags
-  io $ putStrLn $ showSDoc $ vcat $
-    text "packages currently loaded:" 
-    : map (nest 2 . text . packageIdString) 
-               (sortBy (compare `on` packageIdFS) pkg_ids)
   where showFlag (ExposePackage p) = text $ "  -package " ++ p
         showFlag (HidePackage p)   = text $ "  -hide-package " ++ p
         showFlag (IgnorePackage p) = text $ "  -ignore-package " ++ p