Don't try to preserve version of active package.

sdk/lib/_internal/pub/test/global/activate/same_version_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 '../../test_pub.dart';
-
-main() {
-  initConfig();
-  integration('keeps previously activated version if it meets the constraint',
-        () {
-    servePackages([
-      packageMap("foo", "1.2.3"),
-      packageMap("foo", "1.3.0")
-    ]);
-
-    // Activate 1.2.3.
-    schedulePub(args: ["global", "activate", "foo", "1.2.3"]);
-
-    // Activating it again re-resolves but maintains the version.
-    schedulePub(args: ["global", "activate", "foo", ">1.0.0"], output: """
-Package foo is currently active at version 1.2.3.
-Resolving dependencies...
-Activated foo 1.2.3.""");
-  });
-}