How to reproduce:
1. Create a new project
2. Build Xcode project using Default settings (iPad and iPhone Launch screen are set to Default)
3. Examine Xcode project:
3.1 It has black Launch Screen .png files and two XIBs for iPad and iPhone
3.2 info.plist has entry to these files
4. So when you run the project on device you will get black launch screen before Unity splash screen
5. Go back to Unity and set iPhone and iPad Launch Screen to None
6. Add Legacy Launch Images
7. Build Xcode project

Result: Same XIB files are there, info.plist still has entries to these files and running project on device still shows only black launch screen - legacy images are not shown. One has manually change UILaunchStoryboardName entry in info.plist and point to Images.xcassets

Expected result: XIB files should be overridden to match legacy launch screen images or it should be removed and its entry should be removed from info.plist

Reproducible: 2019.3.0a2, 2019.2.0a12, 2019.1.1f1, 2019.1.0a9
Not reproducible: 2019.1.0a1, 2018.3.13f1

Note1: XIBs are overridden to to match legacy launch screen images in version where issue doesn't reproduce
Note2: If first build is created with iPhone and iPad Launch Screen set to None and all Legacy Launch Images added, then issue doesn't reproduce. As XIB files are not created and before Unity splash screen one can see Legacy Launch Images.