two bug fixes. 1.) if analysis through deepd3 is run again, the spines in adata can now be overriden. 2.) There was a bug in DeepD3 where deleted ROIs were removed from self.rois but not self.rois_map. This meant the roi_map we were exporting still included the rois I had deleted. This has now been fixed, so deleted ROIs are empty voxel arrays in self.rois_map. The fix here removes those empty voxel arrays.
