Remove deprecated StringBuffer.add, addAll and addCharCode.

tests/language/call_operator_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.
 
 
 // simple test with no types in signature
 class A1 {
   call() => 42;
 }
 
@@ skipping 14 matching lines @@
 // Test named arguments
 class D {
   call([arg=6]) => 7 * arg;
 }
 
 // Non-trivial method body combination of positional and named.
 class E {
   String call(String str, {int count: 1}) {
     StringBuffer buffer = new StringBuffer();
     for (var i = 0; i < count; i++) {
-      buffer.add(str);
+      buffer.write(str);
       if (i < count - 1) {
-        buffer.add(":");
+        buffer.write(":");
       }
     }
     return buffer.toString();
   }
 }
 
 main() {
   var a1 = new A1();
   Expect.equals(42, a1());
   Expect.equals(42, a1.call());
@@ skipping 22 matching lines @@
   Expect.equals("foo", e("foo"));
   Expect.equals("foo:foo", e("foo", count:2));
   Expect.equals("foo:foo:foo", e("foo", count:3));
   Expect.equals("foo", e.call("foo"));
   Expect.equals("foo:foo", e.call("foo", count:2));
   Expect.equals("foo:foo:foo", e.call("foo", count:3));
 
   Expect.isTrue(a1 is Function);
   Expect.isTrue(e is Function);
 }