Drop support for older Barback versions.

test/run/doesnt_load_an_unnecessary_transformer_test.dart

 // Copyright (c) 2014, the Dart project authors.  Please see the AUTHORS file
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
 import '../descriptor.dart' as d;
 import '../test_pub.dart';
 import '../serve/utils.dart';
 
 const TRANSFORMER = """
 import 'dart:async';
 
 import 'package:barback/barback.dart';
 
 class BrokenTransformer extends Transformer {
   RewriteTransformer.asPlugin() {
     throw 'This transformer is broken!';
   }
 
   String get allowedExtensions => '.txt';
 
   void apply(Transform transform) {}
 }
 """;
 
 main() {
-  withBarbackVersions("any", () {
-    integration("doesn't load an unnecessary transformer", () {
-      d.dir(appPath, [
-        d.pubspec({
-          "name": "myapp",
-          "transformers": [
-            {"myapp/src/transformer": {r"$include": "lib/myapp.dart"}}
-          ]
-        }),
-        d.dir("lib", [
-          d.file("myapp.dart", ""),
-          d.dir("src", [d.file("transformer.dart", TRANSFORMER)])
-        ]),
-        d.dir("bin", [
-          d.file("hi.dart", "void main() => print('Hello!');")
-        ])
-      ]).create();
+  integration("doesn't load an unnecessary transformer", () {
+    d.dir(appPath, [
+      d.pubspec({
+        "name": "myapp",
+        "transformers": [
+          {"myapp/src/transformer": {r"$include": "lib/myapp.dart"}}
+        ]
+      }),
+      d.dir("lib", [
+        d.file("myapp.dart", ""),
+        d.dir("src", [d.file("transformer.dart", TRANSFORMER)])
+      ]),
+      d.dir("bin", [
+        d.file("hi.dart", "void main() => print('Hello!');")
+      ])
+    ]).create();
 
-      createLockFile('myapp', pkg: ['barback']);
+    createLockFile('myapp', pkg: ['barback']);
 
-      // This shouldn't load the transformer, since it doesn't transform
-      // anything that the entrypoint imports. If it did load the transformer,
-      // we'd know since it would throw an exception.
-      var pub = pubRun(args: ["bin/hi"]);
-      pub.stdout.expect("Hello!");
-      pub.shouldExit();
-    });
+    // This shouldn't load the transformer, since it doesn't transform
+    // anything that the entrypoint imports. If it did load the transformer,
+    // we'd know since it would throw an exception.
+    var pub = pubRun(args: ["bin/hi"]);
+    pub.stdout.expect("Hello!");
+    pub.shouldExit();
   });
 }