Get rid of all the library tags.

lib/src/backend/platform_selector.dart

 // Copyright (c) 2015, 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.
 
-library test.backend.platform_selector;
-
 import 'package:source_span/source_span.dart';
 
 import 'operating_system.dart';
 import 'platform_selector/ast.dart';
 import 'platform_selector/evaluator.dart';
 import 'platform_selector/parser.dart';
 import 'platform_selector/visitor.dart';
 import 'test_platform.dart';
 
 /// The set of all valid variable names.
@@ skipping 77 matching lines @@
 /// and it isn't done when parsing to avoid coupling the syntax too tightly to
 /// the semantics.
 class _VariableValidator extends RecursiveVisitor {
   const _VariableValidator();
 
   void visitVariable(VariableNode node) {
     if (_validVariables.contains(node.name)) return;
     throw new SourceSpanFormatException("Undefined variable.", node.span);
   }
 }