Fix all the analysis hints in pub.

sdk/lib/_internal/pub/lib/src/ascii_tree.dart

Index: sdk/lib/_internal/pub/lib/src/ascii_tree.dart
diff --git a/sdk/lib/_internal/pub/lib/src/ascii_tree.dart b/sdk/lib/_internal/pub/lib/src/ascii_tree.dart
index d197df1b574866e43b8c88344fc28750aec4213b..015a6e2c8d25d54170445e7a3419eeab1e0d1dd2 100644
--- a/sdk/lib/_internal/pub/lib/src/ascii_tree.dart
+++ b/sdk/lib/_internal/pub/lib/src/ascii_tree.dart
@@ -65,7 +65,6 @@ String fromFiles(List<String> files, {String baseDir, bool showAllChildren}) {
   var root = {};
   for (var file in files) {
     if (baseDir != null) file = path.relative(file, from: baseDir);
-    var parts = path.split(file);
     var directory = root;
     for (var part in path.split(file)) {
       directory = directory.putIfAbsent(part, () => {});