Bug 1117060 - remove some deprecated let expressions in /im. r=florian, a=mkmelin

im/content/preferences/applications.js

@@ -1042,10 +1042,9 @@ var gApplicationsPane = {
         return this._getIconURLForSystemDefault(aHandlerInfo);
 
       case Ci.nsIHandlerInfo.useHelperApp:
-        let (preferredApp = aHandlerInfo.preferredApplicationHandler) {
+        let preferredApp = aHandlerInfo.preferredApplicationHandler;
         if (this.isValidHandlerApp(preferredApp))
           return this._getIconURLForHandlerApp(preferredApp);
-        }
         break;
 
       // This should never happen, but if preferredAction is set to some weird