Remove unnecessary extendTyVarEnvFVRn function

The `extendTyVarEnvFVRn` function does the exact same thing as
`bindLocalNamesFV`. I see no meaningful distinction between the two functions,
so let's just remove the former (which is only used in a handful of places) in
favor of the latter.

Historical note: `extendTyVarEnvFVRn` and `bindLocalNamesFV` used to be
distinct functions, but their implementations were synchronized in 2004 as a
part of commit 20e39e0e.

compiler/GHC/Rename/Bind.hs

@@ -41,7 +41,7 @@ import GHC.Rename.Pat
 import GHC.Rename.Names
 import GHC.Rename.Env
 import GHC.Rename.Fixity
-import GHC.Rename.Utils ( HsDocContext(..), mapFvRn, extendTyVarEnvFVRn
+import GHC.Rename.Utils ( HsDocContext(..), mapFvRn
                         , checkDupRdrNames, checkDupRdrNamesN, warnUnusedLocalBinds
                         , checkUnusedRecordWildcard
                         , checkDupAndShadowedNames, bindLocalNamesFV
@@ -869,7 +869,7 @@ rnMethodBinds is_cls_decl cls ktv_names binds sigs
              sig_ctxt | is_cls_decl = ClsDeclCtxt cls
                       | otherwise   = InstDeclCtxt bound_nms
        ; (spec_inst_prags', sip_fvs) <- renameSigs sig_ctxt spec_inst_prags
-       ; (other_sigs',      sig_fvs) <- extendTyVarEnvFVRn ktv_names $
+       ; (other_sigs',      sig_fvs) <- bindLocalNamesFV ktv_names $
                                         renameSigs sig_ctxt other_sigs
 
        -- Rename the bindings RHSs.  Again there's an issue about whether the

compiler/GHC/Rename/Module.hs

@@ -32,7 +32,7 @@ import GHC.Rename.Env
 import GHC.Rename.Utils ( HsDocContext(..), mapFvRn, bindLocalNames
                         , checkDupRdrNamesN, bindLocalNamesFV
                         , checkShadowedRdrNames, warnUnusedTypePatterns
-                        , extendTyVarEnvFVRn, newLocalBndrsRn
+                        , newLocalBndrsRn
                         , withHsDocContext, noNestedForallsContextsErr
                         , addNoNestedForallsContextsErr, checkInferredVars )
 import GHC.Rename.Unbound ( mkUnboundName, notInScopeErr )
@@ -628,7 +628,7 @@ rnClsInstDecl (ClsInstDecl { cid_poly_ty = inst_ty, cid_binds = mbinds
        -- Both need to have the instance type variables in scope
        ; traceRn "rnSrcInstDecl" (ppr inst_ty' $$ ppr ktv_names)
        ; ((ats', adts'), more_fvs)
-             <- extendTyVarEnvFVRn ktv_names $
+             <- bindLocalNamesFV ktv_names $
                 do { (ats',  at_fvs)  <- rnATInstDecls rnTyFamInstDecl cls ktv_names ats
                    ; (adts', adt_fvs) <- rnATInstDecls rnDataFamInstDecl cls ktv_names adts
                    ; return ( (ats', adts'), at_fvs `plusFV` adt_fvs) }
@@ -2043,7 +2043,7 @@ rnLDerivStrategy doc mds thing_inside
              -- (Wrinkle: Derived instances) in GHC.Hs.Type.
              addNoNestedForallsContextsErr doc
                (quotes (text "via") <+> text "type") via_body
-             (thing, fvs2) <- extendTyVarEnvFVRn via_tvs thing_inside
+             (thing, fvs2) <- bindLocalNamesFV via_tvs thing_inside
              pure (ViaStrategy via_ty', thing, fvs1 `plusFV` fvs2)
 
     inf_err = Just (text "Inferred type variables are not allowed")

compiler/GHC/Rename/Utils.hs

@@ -25,7 +25,7 @@ module GHC.Rename.Utils (
 
         bindLocalNames, bindLocalNamesFV,
 
-        addNameClashErrRn, extendTyVarEnvFVRn,
+        addNameClashErrRn,
 
         checkInferredVars,
         noNestedForallsContextsErr, addNoNestedForallsContextsErr
@@ -101,11 +101,6 @@ bindLocalNamesFV names enclosed_scope
   = do  { (result, fvs) <- bindLocalNames names enclosed_scope
         ; return (result, delFVs names fvs) }
 
--------------------------------------
-
-extendTyVarEnvFVRn :: [Name] -> RnM (a, FreeVars) -> RnM (a, FreeVars)
-extendTyVarEnvFVRn tyvars thing_inside = bindLocalNamesFV tyvars thing_inside
-
 -------------------------------------
 checkDupRdrNames :: [LocatedN RdrName] -> RnM ()
 -- Check for duplicated names in a binding group