Remove HTMLHtmlElement.manifest

Source/core/frame/UseCounter.cpp

Index: Source/core/frame/UseCounter.cpp
diff --git a/Source/core/frame/UseCounter.cpp b/Source/core/frame/UseCounter.cpp
index 4537d99f1950e1ba15191096706a34e9513a52e9..88988d8657bf402496295fb271b60b2618f3ab13 100644
--- a/Source/core/frame/UseCounter.cpp
+++ b/Source/core/frame/UseCounter.cpp
@@ -694,9 +694,6 @@ String UseCounter::deprecationMessage(Feature feature)
     case PrefixedCancelRequestAnimationFrame:
         return "'webkitCancelRequestAnimationFrame' is vendor-specific. Please use the standard 'cancelAnimationFrame' instead.";
 
-    case HTMLHtmlElementManifest:
-        return "'HTMLHtmlElement.manifest' is deprecated. The manifest attribute only has an effect during the early stages of document load.";
-
     case DocumentCreateAttributeNS:
         return "'Document.createAttributeNS' is deprecated and has been removed from DOM4 (http://w3.org/tr/dom).";