[dartdev] Remove dart build preview note

This went to stable together with the build hooks, but we forgot to
remove this message.

Change-Id: I1e67b479285476629e5a48ee4319d3d6206027c8
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/474821
Auto-Submit: Daco Harkes <dacoharkes@google.com>
Commit-Queue: Daco Harkes <dacoharkes@google.com>
Reviewed-by: Michael Goderbauer <goderbauer@google.com>

pkg/dartdev/lib/src/commands/build.dart

@@ -167,9 +167,6 @@ then that is used instead.''',
     final verbosity = args.option('verbosity')!;
     final enabledExperiments = args.enabledExperiments;
 
-    stdout.writeln('''The `dart build cli` command is in preview at the moment.
-See documentation on https://dart.dev/interop/c-interop#native-assets.
-''');
     final packageConfigUri = await DartNativeAssetsBuilder.ensurePackageConfig(
       sourceUri,
     );