chore: use #lang lean4

src/Lean/Elab/Import.lean

@@ -1,10 +1,10 @@
+#lang lean4
 /-
 Copyright (c) 2019 Microsoft Corporation. All rights reserved.
 Released under Apache 2.0 license as described in the file LICENSE.
 Authors: Leonardo de Moura, Sebastian Ullrich
 -/
 import Lean.Parser.Module
-new_frontend
 namespace Lean.Elab
 
 def headerToImports (header : Syntax) : List Import :=

src/Lean/Elab/LetRec.lean

@@ -1,3 +1,4 @@
+#lang lean4
 /-
 Copyright (c) 2020 Microsoft Corporation. All rights reserved.
 Released under Apache 2.0 license as described in the file LICENSE.
@@ -7,7 +8,6 @@ import Lean.Elab.Attributes
 import Lean.Elab.Binders
 import Lean.Elab.DeclModifiers
 import Lean.Elab.SyntheticMVars
-new_frontend
 namespace Lean.Elab.Term
 open Meta
 

src/Lean/Elab/Level.lean

@@ -1,3 +1,4 @@
+#lang lean4
 /-
 Copyright (c) 2019 Microsoft Corporation. All rights reserved.
 Released under Apache 2.0 license as described in the file LICENSE.
@@ -6,7 +7,6 @@ Authors: Leonardo de Moura
 import Lean.Meta.LevelDefEq
 import Lean.Elab.Exception
 import Lean.Elab.Log
-new_frontend
 
 namespace Lean.Elab.Level
 

src/Lean/Elab/Log.lean

@@ -1,3 +1,4 @@
+#lang lean4
 /-
 Copyright (c) 2019 Microsoft Corporation. All rights reserved.
 Released under Apache 2.0 license as described in the file LICENSE.
@@ -5,7 +6,6 @@ Authors: Leonardo de Moura
 -/
 import Lean.Elab.Util
 import Lean.Elab.Exception
-new_frontend
 
 namespace Lean.Elab