Speed up broken image selector

Using jquery this took 5ms just on the login page:
https://cl.ly/0ffa8030060d
using document.querySelectorAll will be faster

Test plan:
* the broken image fallbacks should work exactly the same as before

Change-Id: I1c38974dbcc55d5f777d48a7603ce847217b0ec6
Reviewed-on: https://gerrit.instructure.com/208615
Tested-by: Jenkins
Reviewed-by: Clay Diffrient <cdiffrient@instructure.com>
QA-Review: Ryan Shaw <ryan@instructure.com>
Product-Review: Ryan Shaw <ryan@instructure.com>

app/coffeescripts/behaviors/broken-images.js

@@ -44,9 +44,7 @@ export function attachErrorHandler(imgElement) {
 }
 
 export function getImagesAndAttach () {
-  $('img[src!=""]')
-    .toArray()
-    .forEach(attachErrorHandler)
+  Array.from(document.querySelectorAll('img:not([src=""])')).forEach(attachErrorHandler)
 }
 
 // this behavior will set up all broken images on the page with an error handler that