fix crash with Kipi-plugins setup from digiKam (not reproducible with KPhotoAlbum)

the problem is not with kipi-plugins, but in digiKam core, especially the way to manage plugin Actions
deletion with Action Collection dedicated to kipi. There is an order to respect.
With this commit i fix also a missing clear of list of plugin action when plugins are replug from manager.
CCBUGS: 265641