Remove support for legacy const, part 1

test/mjsunit/compiler/regress-const.js

 // Copyright 2011 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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-// Flags: --allow-natives-syntax --legacy-const
+// Flags: --allow-natives-syntax
 
 // Test const initialization and assignments.
 function f() {
   var x = 42;
   while (true) {
     const y = x;
     if (--x == 0) return y;
   }
 }
 
 function g() {
   const x = 42;
-  x += 1;
   return x;
 }
 
 for (var i = 0; i < 5; i++) {
   f();
   g();
 }
 
 %OptimizeFunctionOnNextCall(f);
 %OptimizeFunctionOnNextCall(g);
 
-assertEquals(42, f());
+assertEquals(1, f());
 assertEquals(42, g());
 
 
 function h(a, b) {
   var r = a + b;
   const X = 42;
   return r + X;
 }
 
 for (var i = 0; i < 5; i++) h(1,2);
 
 %OptimizeFunctionOnNextCall(h);
 
 assertEquals(45, h(1,2));
 assertEquals("foo742", h("foo", 7));