After importing my Aperture library into Photos, I notice there are now what appears to be some legacy files and folders in the Photos library file structure viewable in Finder when showing package content for Photos Library. Biggest is the folder "iMovie-Thumbnails" which weighs almost 3 GB and consists of a lot of heavily compressed video clips, mostly from movies that I have deleted long ago. The clips are not visible in the Photos app so what's the point? There's also the folder "Aperture.aplib" and the files "ApertureData" and "iPhotoLock.data". What's this? Can I remove any of it?