Remove unused Dictionary forward declaration and include

It seems that these are leftovers when I replaced Dictionary
with IDL dictionaries. Added a forward declaration in
Element.h instead (which is actually using Dictionary).

Review URL: https://codereview.chromium.org/723473002

git-svn-id: svn://svn.chromium.org/blink/trunk@185197 bbb929c8-8fbe-4397-9dbb-9b2b20218538

third_party/WebKit/Source/core/dom/Element.h

@@ -48,6 +48,7 @@ class ClientRectList;
 class CustomElementDefinition;
 class DOMStringMap;
 class DOMTokenList;
+class Dictionary;
 class Document;
 class ElementRareData;
 class ElementShadow;

third_party/WebKit/Source/core/dom/MutationObserver.h

@@ -42,7 +42,6 @@
 
 namespace blink {
 
-class Dictionary;
 class ExceptionState;
 class MutationCallback;
 class MutationObserver;

third_party/WebKit/Source/core/html/canvas/HitRegion.h

@@ -5,7 +5,6 @@
 #ifndef HitRegion_h
 #define HitRegion_h
 
-#include "bindings/core/v8/Dictionary.h"
 #include "core/dom/Element.h"
 #include "core/html/canvas/HitRegionOptions.h"
 #include "platform/graphics/Path.h"