Remove case causing too much recursion in metrics pings (#460)

- fixes #455
- fixes #457

lib/send-metrics-data.js

@@ -4,18 +4,14 @@ const {Cu} = require('chrome');
 Cu.import('resource://gre/modules/Services.jsm');
 
 const { getActiveView } = require('sdk/view/core');
-const { setTimeout } = require('sdk/timers');
 
 module.exports = sendMetricsData;
 
 function sendMetricsData(o, panel) {
   // Note: panel is optional, used to avoid circular refs with panel-utils.js.
   panel = panel || require('./panel-utils.js').getPanel();
 
-  // If the panel's missing, try again a few seconds later.
-  if (!panel) {
-    return setTimeout(() => { sendMetricsData(o) }, 10 * 1000);
-  }
+  if (!panel) return;
 
   const coords = getActiveView(panel).getBoundingClientRect();
   // NOTE: this packet follows a predefined data format and cannot be changed