Remove unimplemented registerExtensionPrefix API

resource/feeds/FeedProcessor.js

@@ -173,10 +173,6 @@ FeedResult.prototype = {
 	headers: null,
 	uri: null,
 	stylesheet: null,
-	
-	registerExtensionPrefix: function (ns, prefix) {
-		throw Cr.NS_ERROR_NOT_IMPLEMENTED;
-	},
 };
 
 // Implements nsIFeed, nsIFeedContainer

resource/feeds/nsIFeedContainer.idl

@@ -31,7 +31,6 @@ interface nsIFeedContainer : nsIFeedElementBase
 	* and accessing specific fields.
 	*
 	* Common namespaces are accessed using prefixes, like get("dc:subject");.
-	* See nsIFeedResult::registerExtensionPrefix.
 	*/
 	attribute nsIWritablePropertyBag2 fields;
 

resource/feeds/nsIFeedResult.idl

@@ -56,9 +56,4 @@ interface nsIFeedResult : nsISupports {
 	* HTTP response headers that accompanied the feed. 
 	*/
 	attribute nsIProperties headers;
-
-	/**
-	* Registers a prefix used to access an extension in the feed/entry 
-	*/
-	void registerExtensionPrefix(in AString aNamespace, in AString aPrefix);
 };