how can you remove it from the source
Photoshop is not part of your source. A user does not need Photoshop to open your project in Unity.
ok but you sad "you can use Gaia to create your terrain in Unity, but you must delete Gaia out of your project when uploading the source."
so how can i delete it from the source?
At this point I recommend just uploading whatever is needed to open your game in Unity when you submit to the jam. During my source verification check I will let you know if you need to remove any paid assets from your project.
ok thanks for all your help
