Remove unnecessary imports from front_end

Bug: #44569
Change-Id: I646f5994b40f2007f8d8d4b5ef35e2c9ffbd2376
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/213423
Auto-Submit: Samuel Rawlins <[email protected]>
Reviewed-by: Johnni Winther <[email protected]>
Commit-Queue: Johnni Winther <[email protected]>

Author: srawlins

pkg/front_end/lib/src/fasta/kernel/constructor_tearoff_lowering.dart

@@ -6,7 +6,6 @@ import 'package:kernel/ast.dart';
 import 'package:kernel/type_algebra.dart';
 import '../builder/member_builder.dart';
 import '../source/source_library_builder.dart';
-import 'kernel_api.dart';
 import 'kernel_helper.dart';
 
 const String _tearOffNamePrefix = '_#';