Remove library tags, they aren't needed

lib/src/codegen/js_printer.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 dev_compiler.src.codegen.js_printer;
-
 import 'dart:convert' show JSON, JsonEncoder;
 import 'dart:io' show Directory, File, Platform, Process;
 
 import 'package:analyzer/src/generated/ast.dart';
 import 'package:path/path.dart' as path;
 import 'package:source_maps/source_maps.dart' as srcmaps show Printer;
 import 'package:source_maps/source_maps.dart' show SourceMapSpan;
 import 'package:source_span/source_span.dart' show SourceLocation;
 
 import '../js/js_ast.dart' as JS;
@@ skipping 130 matching lines @@
       _currentTopLevelDeclaration == null;
       return;
     }
   }
 
   String _getIdentifier(AstNode node) {
     if (node is SimpleIdentifier) return node.name;
     return null;
   }
 }