Remove an obsolete reference to proxyquireify

Even though the linked issue no longer applies, this module is never
used outside the sidebar app so there is no concern with it having
sidebar app-specific dependencies.

src/sidebar/raven.js

@@ -13,13 +13,6 @@
  */
 
 const Raven = require('raven-js');
-
-// This is only used in apps where Angular is used,
-// but is required globally due to
-// https://github.com/thlorenz/proxyquireify/issues/40
-//
-// Fortunately it does not pull in Angular as a dependency but returns
-// a function that takes it as an input argument.
 const angularPlugin = require('raven-js/plugins/angular');
 
 /**