Remove unnecessary check in RegExpExecStub.

test/mjsunit/regexp-stack-overflow.js

+// Copyright 2014 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: --stack-size=100
+
+var result = null;
+var type = true;
+var re = /\w/;
+re.test("a");  // Trigger regexp compile.
+
+function rec() {
+  try {
+    return rec();
+  } catch (e) {
+    if (!(e instanceof RangeError)) type = false;
+    return re.test("b");
+  }
+}
+
+assertTrue(rec());
+assertTrue(type);