Remove deprecated string features.

tests/corelib/core_runtime_types_test.dart

 // Copyright (c) 2011, 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.
 
 /**
  * A test of simple runtime behavior on numbers, strings and lists with
  * a focus on both correct behavior and runtime errors.
  *
  * This file is written to use minimal type declarations to match a
  * typical dynamic language coding style.
@@ skipping 135 matching lines @@
     } catch (e) { }
     try {
       y.toRadixString(-1);
       Expect.fail("Illegal radix -1 accepted.");
     } catch (e) { }
   }
 
   static testStringOperators() {
     var s = "abcdef";
     assertEquals(s, "abcdef");
-    assertEquals(s.charCodeAt(0), 97);
+    assertEquals(s.codeUnitAt(0), 97);
     assertEquals(s[0], 'a');
     assertEquals(s.length, 6);
     assertTypeError(() { s[null]; });
     assertTypeError(() { s['hello']; });
     assertTypeError(() { s[0] = 'x'; });
   }
 
   // TODO(jimhug): Fill out full set of string methods.
   static testStringMethods() {
     var s = "abcdef";
@@ skipping 107 matching lines @@
     '${true}'.toString();
     '${false}'.toString();
     ''.toString();
     ''.endsWith('');
   }
 }
 
 main() {
   CoreRuntimeTypesTest.testMain();
 }