Bug 1484153 - Drop duplicate outerWindowID logging in listener.js. r=whimboo

When receiving observer notifications during navigation, we log the
outerWindowID:

	logger.debug(`Received observer notification ${topic} for ${winID}`);

This is no longer necessary as
https://bugzilla.mozilla.org/show_bug.cgi?id=1464469 introduced the
outerWindowID as a prefix to all log messages originating from this
frame script.

testing/marionette/listener.js

@@ -344,7 +344,7 @@ const loadListener = {
     const winID = subject.QueryInterface(Ci.nsISupportsPRUint64).data;
     const curWinID = win.windowUtils.outerWindowID;
 
-    logger.debug(`Received observer notification ${topic} for ${winID}`);
+    logger.debug(`Received observer notification ${topic}`);
 
     switch (topic) {
       // In the case when the currently selected frame is closed,