The UI list and asset view preview size calculations were out of sync,
so the UI list made more space than the preview actually used. Making
them match made the previews quite large though, so compensate that by
scaling the layout down.
Remove the related TODO comment, since this uses a common function for
getting the preview size now.
Before/after:
 
Pull Request: https://projects.blender.org/blender/blender/pulls/108017
d4217c278e