Remove support for legacy const, part 1

test/mjsunit/regress/regress-88591.js

 // Copyright 2011 the V8 project authors. All rights reserved.
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-// Flags: --legacy-const
-
 // Regression test for a crash.  A data property in the global object's
 // prototype shadowed by a setter in the global object's prototype's
 // prototype would crash or assert when seen by Runtime_DeclareContextSlot.
 var called = false;
 Object.prototype.__defineSetter__('x', function(x) { called = true; });
 Object.prototype.__defineGetter__('x', function () { return 0; });
 
 this.__proto__ = { x: 1 };
 
-try { fail; } catch (e) { eval('const x = 2'); }
+try { fail; } catch (e) { eval('var x = 2'); }
 
 var o = Object.getOwnPropertyDescriptor(this, 'x');
 assertFalse(called);
 assertEquals(2, o.value);
-assertEquals(false, o.writable);
+assertEquals(true, o.writable);