Remove duplicate batch progress module

* Batch progress is started in application.html.erb, this created a
second module which duplicated requests, and may have caused some of
the weird differences between flash message and modal
Remove elements on batch success

* Remove message about “continuing”, the progress spinner and the
progress bar when a batch succeeds
* Move logic out of CSS and into JS using js- prefixed classes
Merge pull request #270 from alphagov/remove-message-on-bulk-complete

Remove helpful message when background process succeeds