[BUGFIX] RTE: Image drag & drop raises PHP error

Old class name was left over.

Releases: master
Resolves: #64649
Change-Id: Ie78c781d466e6fabfc11170d828a9e43544bad65
Reviewed-on: http://review.typo3.org/36640


Reviewed-by: Stanislas Rolland <typo3@sjbr.ca>
Tested-by: Stanislas Rolland <typo3@sjbr.ca>