Drop support for older Barback versions.

test/transformer/can_use_read_input_as_string_test.dart

 // Copyright (c) 2013, the Dart project authors.  Please see the AUTHORS d.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.
 
 library pub_tests;
 
 import '../descriptor.dart' as d;
 import '../test_pub.dart';
 import '../serve/utils.dart';
 
@@ skipping 11 matching lines @@
     return transform.readInputAsString(transform.primaryInput.id)
         .then((contents) {
       var id = transform.primaryInput.id.changeExtension(".out");
       transform.addOutput(new Asset.fromString(id, "\$contents.out"));
     });
   }
 }
 """;
 
 main() {
-  withBarbackVersions("any", () {
-    integration("a transform can use readInputAsString", () {
-      d.dir(appPath, [
-        d.pubspec({
-          "name": "myapp",
-          "transformers": ["myapp/src/transformer"]
-        }),
-        d.dir("lib", [d.dir("src", [
-          d.file("transformer.dart", TRANSFORMER)
-        ])]),
-        d.dir("web", [
-          d.file("foo.txt", "foo")
-        ])
-      ]).create();
+  integration("a transform can use readInputAsString", () {
+    d.dir(appPath, [
+      d.pubspec({
+        "name": "myapp",
+        "transformers": ["myapp/src/transformer"]
+      }),
+      d.dir("lib", [d.dir("src", [
+        d.file("transformer.dart", TRANSFORMER)
+      ])]),
+      d.dir("web", [
+        d.file("foo.txt", "foo")
+      ])
+    ]).create();
 
-      createLockFile('myapp', pkg: ['barback']);
+    createLockFile('myapp', pkg: ['barback']);
 
-      pubServe();
-      requestShouldSucceed("foo.out", "foo.out");
-      endPubServe();
-    });
+    pubServe();
+    requestShouldSucceed("foo.out", "foo.out");
+    endPubServe();
   });
 }