[turbofan] Remove over-restrictive DCHECKs.

test/mjsunit/regress/regress-crbug-685050.js

+// Copyright 2017 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
+
+function bar(a) {
+  a[0] = 0;
+  a[1] = 0;
+}
+
+var a = new Int32Array(2);
+bar([1, 2, 3]);
+function foo() {
+  bar([1, 2, 3]);
+  bar(a);
+}
+%OptimizeFunctionOnNextCall(foo);
+foo();