[turbofan] Remove deprecated --turbo-osr flag.

test/mjsunit/compiler/osr-forin.js

 // Copyright 2015 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: --use-osr --turbo-osr
+// Flags: --use-osr
 
 function f(a) {
   var sum = 0;
   for (var j in a) {
     var i = a[j];
     var x = i + 2;
     var y = x + 5;
     var z = y + 3;
     sum += z;
   }
   return sum;
 }
 
 var a = new Array(10000);
 for (var i = 0; i < 10000; i++) {
   a[i] = (i * 999) % 77;
 }
 
 for (var i = 0; i < 3; i++) {
   assertEquals(480270, f(a));
 }