Remove code reporting issues with Safe Haskell and coerce.

This is a followup to the fix for #8827, and should be merged
with that change.

(cherry picked from commit 7602bd4d)

compiler/typecheck/TcErrors.lhs

@@ -995,9 +995,8 @@ mk_dict_err ctxt (ct, (matches, unifiers, safe_haskell))
   = do { let (is_ambig, ambig_msg) = mkAmbigMsg ct
        ; (ctxt, binds_msg) <- relevantBindings True ctxt ct
        ; traceTc "mk_dict_err" (ppr ct $$ ppr is_ambig $$ ambig_msg)
-       ; safe_mod <- safeLanguageOn `fmap` getDynFlags
        ; rdr_env <- getGlobalRdrEnv
-       ; return (ctxt, cannot_resolve_msg safe_mod rdr_env is_ambig binds_msg ambig_msg) }
+       ; return (ctxt, cannot_resolve_msg rdr_env is_ambig binds_msg ambig_msg) }
 
   | not safe_haskell   -- Some matches => overlap errors
   = return (ctxt, overlap_msg)
@@ -1012,8 +1011,8 @@ mk_dict_err ctxt (ct, (matches, unifiers, safe_haskell))
     givens      = getUserGivens ctxt
     all_tyvars  = all isTyVarTy tys
 
-    cannot_resolve_msg safe_mod rdr_env has_ambig_tvs binds_msg ambig_msg
-      = vcat [ addArising orig (no_inst_msg $$ coercible_explanation safe_mod rdr_env)
+    cannot_resolve_msg rdr_env has_ambig_tvs binds_msg ambig_msg
+      = vcat [ addArising orig (no_inst_msg $$ coercible_explanation rdr_env)
              , vcat (pp_givens givens)
              , ppWhen (has_ambig_tvs && not (null unifiers && null givens))
                (vcat [ ambig_msg, binds_msg, potential_msg ])
@@ -1138,27 +1137,12 @@ mk_dict_err ctxt (ct, (matches, unifiers, safe_haskell))
     -- This function tries to reconstruct why a "Coercible ty1 ty2" constraint
     -- is left over. Therefore its logic has to stay in sync with
     -- getCoericbleInst in TcInteract. See Note [Coercible Instances]
-    coercible_explanation safe_mod rdr_env
+    coercible_explanation rdr_env
       | clas /= coercibleClass = empty
       | Just (tc1,tyArgs1) <- splitTyConApp_maybe ty1,
         Just (tc2,tyArgs2) <- splitTyConApp_maybe ty2,
         tc1 == tc2
       = nest 2 $ vcat $
-          -- Only for safe haskell: First complain if tc is abstract, only if
-          -- not check if the type constructors therein are abstract
-          (if safe_mod
-           then case tyConAbstractMsg rdr_env tc1 empty of
-                    Just msg ->
-                       [ msg $$ ptext (sLit "as required in SafeHaskell mode") ]
-                    Nothing ->
-                       [ msg
-                       | tc <- tyConsOfTyCon tc1
-                       , Just msg <- return $
-                           tyConAbstractMsg rdr_env tc $
-                             parens $ ptext (sLit "used within") <+> quotes (ppr tc1)
-                       ]
-           else []
-          ) ++
           [ fsep [ hsep [ ptext $ sLit "because the", speakNth n, ptext $ sLit "type argument"]
                  , hsep [ ptext $ sLit "of", quotes (ppr tc1), ptext $ sLit "has role Nominal,"]
                  , ptext $ sLit "but the arguments"