*: remove remaining bits of old PDF preview

The action was removed in 6dce55b0 (dms: drop PDF thumbnail view, 2021-06-01)
but some CSS declarations were not removed.

Also remove some old commented out javascript that was referencing the
old PDF preview
6 jobs for master in 0 seconds
Status Job ID Name Coverage
  External
passed ERP5.CodingStyleTest-Master

00:50:29

passed ERP5.PerformanceTest-Master

00:26:06

failed ERP5.UnitTest-Master

failed ERP5.UnitTest-Master.Medusa

passed SlapOS.Eggs.UnitTest-Master.Python2

passed SlapOS.Eggs.UnitTest-Master.Python3