Revert "Implement call operator."

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;
+  operator call() => 42;
 }
 
 // same test, include return type
 class A2 {
-  int call() => 35;
+  int operator call() => 35;
 }
 
 class B {
-  call() => 28;
+  call() => 28; // expect warning, should use 'operator call'
 }
 
 // A call() operator can have any arity
 class C {
-  call(arg) => 7 * arg;
+  operator call(arg) => 7 * arg;
 }
 
 // Test named arguments
 class D {
-  call([arg=6]) => 7 * arg;
+  operator call([arg=6]) => 7 * arg;
 }
 
-// Non-trivial method body combination of positional and named.
+// non-trvial method body combination of positional and named
 class E {
-  String call(String str, [int count=1]) {
-    StringBuffer buffer = new StringBuffer();
+  String operator call(String str, [int count=1]) {
+    String result = "";
     for (var i = 0; i < count; i++) {
-      buffer.add(str);
-      if (i < count - 1) {
-        buffer.add(":");
+      result += str;
+      if (i < count -1) {
+        result += ':';
       }
     }
-    return buffer.toString();
+    return result;
   }
 }
 
 main() {
   var a1 = new A1();
   Expect.equals(42, a1());
   Expect.equals(42, a1.call());
 
   var a2 = new A2();
   Expect.equals(35, a2());
@@ skipping 16 matching lines @@
   Expect.equals(14, d.call(arg:2));
 
   var e = new E();
   Expect.equals("foo", e("foo"));
   Expect.equals("foo:foo", e("foo", 2));
   Expect.equals("foo:foo:foo", e("foo", count:3));
   Expect.equals("foo", e.call("foo"));
   Expect.equals("foo:foo", e.call("foo", 2));
   Expect.equals("foo:foo:foo", e.call("foo", count:3));
 }