Forward-port background file deletion
In bd59ca32, an API new to VLCMediaLibraryKit 0.11.0 is deployed to delete locally stored files on the background thread. This is done to prevent the watchdog daemon from killing VLC while deleting large number of media.
This fix must be backported to the 0.10.x branch of VLCMediaLibraryKit and the stable VLC-iOS branch as it is the N°2 in overall crashes in the current release series.