Reverting the Sanitizer commit in case we have to do something urgent

before we deploy it early next week. It's in the branch `sanitizer` for
now.

This reverts commit 9e93d8ed52.

test/javascripts/test_helper.js

@@ -25,6 +25,7 @@
 //= require LAB.js
 //= require Markdown.Converter.js
 //= require Markdown.Editor.js
+//= require Markdown.Sanitizer.js
 //= require better_markdown.js
 //= require bootbox.js
 //= require bootstrap-alert.js