Revert "[BUGFIX] Improve confirmation dialog in drag'n'drop fileupload"

This reverts commit 495afb59

The patch is reverted because it does not work when there is paging in 
the filelist or a file has no thumb shown.
Further the filename canonicalization done by the storage driver is 
not respected when checking the new file name.

Change-Id: I6f4b91bbf28e7b6f0cb8d7bcfb42f0cfb5eeacc6
Reviewed-on: https://review.typo3.org/27158
Reviewed-by: Steffen Ritter
Tested-by: Steffen Ritter