[tests] Cleanup tests that use assertOptimized()/assertUnoptimized().

test/mjsunit/regress/regress-v8-5697.js

 // Copyright 2016 the V8 project authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
-// Flags: --allow-natives-syntax
+// Flags: --allow-natives-syntax --crankshaft
 
 function load(o) { return o.x; }
 
 for (var x = 0; x < 1000; ++x) {
   load({x});
   load({x});
   try { load(); } catch (e) { }
 }
 
 assertOptimized(load);
 
 
 function store(o) { o.x = -1; }
 
 for (var x = 0; x < 1000; ++x) {
   store({x});
   store({x});
   try { store(); } catch (e) { }
 }
 
 assertOptimized(store);