Avoid sending KDirNotify::emitFilesAdded when the emptytrashjob finishes

Summary:
D23650 added an empty trash check in trash fileRemoved triggering KDirNotify::emitFilesChanged.
Making the notification in emptytrashjob redundant and less prescise.
The two changes allow users to have reliable FilesChanged event when the trash is emptied whether by emptytrashjob or individual file deletion.

Needed for D23668

Reviewers: broulik, ngraham

Reviewed By: ngraham

Subscribers: elvisangelaccio, kde-frameworks-devel

Tags: Frameworks

Differential Revision: https://phabricator.kde.org/D23851