Remove redundant imports

Each of these imports removed is redundant with
'package:kernel/ast.dart'.

Bug: #44569
Change-Id: Ia9bc08b4ffd863572c84fe8a4fa465d2e8e04f7c
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/213845
Reviewed-by: Jens Johansen <[email protected]>
Commit-Queue: Samuel Rawlins <[email protected]>

Author: srawlins

pkg/kernel/bin/split.dart

@@ -8,7 +8,6 @@ import 'dart:io';
 
 import 'package:kernel/ast.dart';
 import 'package:kernel/binary/ast_to_binary.dart';
-import 'package:kernel/kernel.dart';
 import 'package:kernel/src/tool/command_line_util.dart';
 
 void usage() {

pkg/kernel/lib/transformations/empty.dart

@@ -5,7 +5,6 @@
 library kernel.transformations.empty;
 
 import '../ast.dart';
-import '../kernel.dart';
 
 Component transformComponent(Component component) {
   new EmptyTransformer().visitComponent(component);

pkg/kernel/lib/transformations/scanner.dart

@@ -5,7 +5,6 @@
 library kernel.transformations.scanner;
 
 import '../ast.dart';
-import '../kernel.dart';
 
 abstract class Scanner<X extends TreeNode?, Y extends TreeNode?> {
   final Scanner<Y, TreeNode?>? next;

pkg/kernel/lib/transformations/value_class.dart

@@ -7,7 +7,6 @@ library kernel.transformations.value_class;
 import 'package:kernel/type_environment.dart';
 
 import '../ast.dart';
-import '../kernel.dart';
 import '../core_types.dart' show CoreTypes;
 import '../class_hierarchy.dart' show ClassHierarchy;
 import './scanner.dart';