Remove redundant import from _js_interop_checks

Bug: #44569
Change-Id: I6fa385eddc76397ce4944674bd548a16755f265d
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/213850
Auto-Submit: Samuel Rawlins <[email protected]>
Commit-Queue: Riley Porter <[email protected]>
Reviewed-by: Riley Porter <[email protected]>

Author: srawlins

pkg/_js_interop_checks/lib/src/transformations/js_util_optimizer.dart

@@ -6,7 +6,6 @@ import 'package:kernel/ast.dart';
 import 'package:kernel/class_hierarchy.dart';
 import 'package:kernel/core_types.dart';
 import 'package:kernel/type_environment.dart';
-import 'package:kernel/kernel.dart';
 
 /// Replaces js_util methods with inline calls to foreign_helper JS which
 /// emits the code as a JavaScript code fragment.