removed obsolete code

lib/single-file/frame-tree.js

@@ -55,7 +55,6 @@ this.frameTree = this.frameTree || (() => {
 		windowId = message.windowId;
 		const frameElements = document.querySelectorAll("iframe, frame, object[type=\"text/html\"][data]");
 		if (window != top) {
-			sessions.set(message.sessionId, { frames: [] });
 			const docData = docHelper.preProcessDoc(document, window, message.options);
 			const content = docHelper.serialize(document);
 			docHelper.postProcessDoc(document, window, message.options);