Remove deprecated string features.

tests/language/static_inline_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.
 
 // Test inlining of assignments in parameter passing. If [StringScanner.charAt]
 // is inlined, the argument expresion [: ++byteOffset :] should not be
 // duplicated.
 
 class StringScanner {
   static String string;
   int byteOffset = -1;
 
   int nextByte(foo) {
     if (foo) return -2;
     return charAt(++byteOffset);
   }
 
   static int charAt(index)
-      => (string.length > index) ? string.charCodeAt(index) : -1;
+      => (string.length > index) ? string.codeUnitAt(index) : -1;
 }
 
 void main() {
   var scanner = new StringScanner();
   StringScanner.string = 'az9';
   Expect.equals(0x61, scanner.nextByte(false)); // Expect a.
   Expect.equals(0x7A, scanner.nextByte(false)); // Expect z.
   Expect.equals(0x39, scanner.nextByte(false)); // Expect 9.
   Expect.equals(-1, scanner.nextByte(false));
-}
+}