klipper: avoid creating too many KIO::DeleteJob when clearing history to fix potential crash
Reason for the change
If there are many items in the clipboard history, when clearing the whole history, the number of KIO::DeleteJob will crash plasmashell. This uses the QList overload to create KIO::DeleteJob so the number of jobs is controlled at a reasonable level.
Test plan
Clear the history and ~/.local/share/klipper/data folder should become empty