Remove old #import, #source, and #library syntax from tests/standalone.

tests/standalone/io/file_test.dart

 // Copyright (c) 2012, 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.
 //
 // Dart test program for testing file I/O.
 
-#import("dart:io");
-#import("dart:isolate");
+import "dart:io";
+import "dart:isolate";
 
 class MyListOfOneElement implements List {
   int _value;
   MyListOfOneElement(this._value);
   int get length => 1;
   operator [](int index) => _value;
 }
 
 class FileTest {
   static Directory tempDirectory;
@@ skipping 1309 matching lines @@
       testDirectorySync();
       testWriteStringUtf8();
       testWriteStringUtf8Sync();
     });
   }
 }
 
 main() {
   FileTest.testMain();
 }