Remove the thumbnail from the Item Record

[JessWaggs]

All of the users preferred only including the embedded video in the Item Record display

YouTube Usability Report item 2.3.1.2

[NedHenry]

Fixed in 21d34c1, both for public and admin views. The imported thumbnail file is stored in the metadata element "Imported Thumbnail", to distinguish it from any other files that might be added to the item. Then, javascript hides this element from admin and public views in most standard themes.