Minor LeanConfig code cleanup

Lake/LeanConfig.lean

@@ -1,13 +1,12 @@
-
 /-
 Copyright (c) 2021 Mac Malone. All rights reserved.
 Released under Apache 2.0 license as described in the file LICENSE.
 Authors: Mac Malone
 -/
-import Lean
+import Lean.Elab.Frontend
 import Lake.Package
 
-open Lean Elab System
+open Lean System
 
 namespace Lake
 
@@ -17,7 +16,7 @@ namespace PackageConfig
 
 unsafe def fromLeanFileUnsafe (path : FilePath) : IO PackageConfig := do
   let input ← IO.FS.readFile path
-  let (env, ok) ← runFrontend input Options.empty path.toString `package
+  let (env, ok) ← Elab.runFrontend input Options.empty path.toString `package
   if ok then
     IO.ofExcept <| Id.run <| ExceptT.run <|
       env.evalConstCheck PackageConfig Options.empty ``PackageConfig `package