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

test/mjsunit/regress/regress-crbug-480807.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: --allow-natives-syntax --use-osr --turbo-osr --noalways-opt
+// Flags: --allow-natives-syntax --use-osr --noalways-opt
 
 function foo() {
   var c = 0;
   for (var e = 0; e < 1; ++e) {
     for (var a = 1; a > 0; a--) {
       c += 1;
     }
     for (var b = 1; b > 0; b--) {
       %OptimizeOsr();
     }
   }
   return c;
 }
 try {
   foo();
 } catch (e) {
 }