Simplify equality checks and get rid of unreachable code in number and bool.

compiler/lib/implementation/bool.js

 // 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.
 
 function native_BoolImplementation_EQ(other) {
-  return typeof other == 'boolean' && this == other;
+  throw Error('UNREACHABLE');
 }
 
 function native_BoolImplementation_toString() {
   return this.toString();
 }
 
 function native_BoolImplementation_toBool() {
   return this == true;
 }