VM: Remove unnecessary imports

TEST=Existing tests on existing bots

Bug: #44569
Change-Id: I0c8ee9afa85da3a1a39a983841e62956e76dd509
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/177242
Commit-Queue: Samuel Rawlins <[email protected]>
Reviewed-by: Johnni Winther <[email protected]>

Author: srawlins

pkg/vm/bin/kernel_service.dart

@@ -44,8 +44,6 @@ import 'package:vm/kernel_front_end.dart'
     show autoDetectNullSafetyMode, createLoadedLibrariesSet;
 import 'package:vm/http_filesystem.dart';
 import 'package:vm/target/vm.dart' show VmTarget;
-import 'package:front_end/src/api_prototype/compiler_options.dart'
-    show CompilerOptions, parseExperimentalFlags;
 
 final bool verbose = new bool.fromEnvironment('DFE_VERBOSE');
 final bool dumpKernel = new bool.fromEnvironment('DFE_DUMP_KERNEL');