[intl] Remove redundant type checking system

test/intl/bad-target.js

+// Copyright 2016 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.
+
+// Calling Intl methods with a bad receiver throws a TypeError
+
+// An uninitialized object of the same type
+assertThrows(() => Object.create(Intl.DateTimeFormat.prototype).format(),
+             TypeError);
+assertThrows(() => Object.create(Intl.NumberFormat.prototype).format(),
+             TypeError);
+assertThrows(() => Object.create(Intl.Collator.prototype).compare(),
+             TypeError);
+assertThrows(() => Object.create(Intl.v8BreakIterator.prototype).adoptText(),
+             TypeError);
+assertThrows(() => Object.create(Intl.v8BreakIterator.prototype).first(),
+             TypeError);
+assertThrows(() => Object.create(Intl.v8BreakIterator.prototype).next(),
+             TypeError);
+assertThrows(() => Object.create(Intl.v8BreakIterator.prototype).current(),
+             TypeError);
+assertThrows(() => Object.create(Intl.v8BreakIterator.prototype).breakType(),
+             TypeError);
+
+// Or similarly, just accessing the method getter on the prototype
+assertThrows(() => Intl.DateTimeFormat.prototype.format, TypeError);
+assertThrows(() => Intl.NumberFormat.prototype.format, TypeError);
+assertThrows(() => Intl.Collator.prototype.compare, TypeError);
+assertThrows(() => Intl.v8BreakIterator.prototype.adoptText, TypeError);
+assertThrows(() => Intl.v8BreakIterator.prototype.first, TypeError);
+assertThrows(() => Intl.v8BreakIterator.prototype.next, TypeError);
+assertThrows(() => Intl.v8BreakIterator.prototype.current, TypeError);
+assertThrows(() => Intl.v8BreakIterator.prototype.breakType, TypeError);
+
+// The method .call'd on a different instance will have that
+// other instance benignly ignored, since it's a bound function
+let nf = Intl.NumberFormat();
+let df = Intl.DateTimeFormat();
+assertEquals("0", nf.format.call(df, 0));