Deleting folder does not remove subfolder colors

[KoBeWi]

Tested versions

4.3 dev5
Since folder colors were introduced

System information

Windows 10.0.19045 - Vulkan (Forward+) - dedicated NVIDIA GeForce GTX 1060 (NVIDIA; 31.0.15.4633) - Intel(R) Core(TM) i7-7700HQ CPU @ 2.80GHz (8 Threads)

Issue description

In this example:

If you delete yellow Test, its color entry will be gone from projects settings. However, green Test color will remain, even if the folder is gone too.

Steps to reproduce

1. Create folder
2. Set folder color
3. Create folder under the first one
4. Set it a different color
5. Delete parent folder
6. Check project.godot

Minimal reproduction project (MRP)

N/A