Ensure mjsunit tests use dashes not underscores in flags directives.

test/mjsunit/regress/regress-2653.js

 // Copyright 2013 the V8 project authors. All rights reserved.
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 // modification, are permitted provided that the following conditions are
 // met:
 //
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 //       notice, this list of conditions and the following disclaimer.
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 //       with the distribution.
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 //       contributors may be used to endorse or promote products derived
 //       from this software without specific prior written permission.
 //
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-// Flags: --allow-natives-syntax --deopt_every_n_garbage_collections=1
+// Flags: --allow-natives-syntax --deopt-every-n-garbage-collections=1
 
 function foo(a, b) {
   var l = a.length;
   var array = new Array(l);
   for (var k = 0; k < l; k++) {
     array[k] = 120;
   }
   var result = new Array(l);
   for (var i = 0; i < l; i++) {
     result[i] = array[i];
   }
   return result;
 }
 
 a = "xxxxxxxxxxxxxxxxxxxxxxxxx";
 while (a.length < 100000) a = a + a;
 foo(a, []);
 %OptimizeFunctionOnNextCall(foo)
 foo(a, []);