remove file preview thumbnail view

We decided to get rid of thumbnail previews.

fixes CNVS-17158

Test Steps
Given I have multiple files uploaded
And I am a user with new files enabled
When I go to new files
And I preview a file
Then I should NOT seet a "show" or "hide" tab
And there should not be any thumbnails to preview

Change-Id: I77737cd4728050c1b11cd94e85961c4233ffd941
Reviewed-on: https://gerrit.instructure.com/45067
QA-Review: Jahnavi Yetukuri <jyetukuri@instructure.com>
Reviewed-by: Dan Minkevitch <dan@instructure.com>
Tested-by: Jenkins <jenkins@instructure.com>
Product-Review: Ryan Shaw <ryan@instructure.com>