Removed the redundant !this check (fix Clang's -Wundefined-bool-conversion warning)

Source/core/html/HTMLElement.cpp

 /*
  * Copyright (C) 1999 Lars Knoll (knoll@kde.org)
  *           (C) 1999 Antti Koivisto (koivisto@kde.org)
  * Copyright (C) 2004, 2005, 2006, 2007, 2008 Apple Inc. All rights reserved.
  * Copyright (C) 2009 Torch Mobile Inc. All rights reserved. (http://www.torchmobile.com/)
  * Copyright (C) 2011 Motorola Mobility. All rights reserved.
  *
  * This library is free software; you can redistribute it and/or
  * modify it under the terms of the GNU Library General Public
  * License as published by the Free Software Foundation; either
@@ skipping 416 matching lines @@
     RefPtr<Node> next = nextSibling();
     RefPtr<Node> newChild;
 
     // Convert text to fragment with <br> tags instead of linebreaks if needed.
     if (text.contains('\r') || text.contains('\n'))
         newChild = textToFragment(text, exceptionState);
     else
         newChild = Text::create(document(), text);
 
     // textToFragment might cause mutation events.
-    if (!this || !parentNode())
+    if (!parentNode())
         exceptionState.throwDOMException(HierarchyRequestError, "The element has no parent.");
 
     if (exceptionState.hadException())
         return;
 
     parent->replaceChild(newChild.release(), this, exceptionState);
 
     RefPtr<Node> node = next ? next->previousSibling() : 0;
     if (!exceptionState.hadException() && node && node->isTextNode())
         mergeWithNextTextNode(node.release(), exceptionState);
@@ skipping 520 matching lines @@
 #ifndef NDEBUG
 
 // For use in the debugger
 void dumpInnerHTML(WebCore::HTMLElement*);
 
 void dumpInnerHTML(WebCore::HTMLElement* element)
 {
     printf("%s\n", element->innerHTML().ascii().data());
 }
 #endif