Initial Terrain Layer is used for Painting Texture and will be added to the Terrain Layer List after being replaced by another Terrain Layer

Steps to reproduce:

1. Open any Project
2. Create a Terrain Game Object in a Scene, create 2 Terrain Layers in the Project Browser
3. Select the Terrain Game Object and in the Inspector switch the Terrain Component's Mode to Paint Texture
4. Click on the "Edit Terrain Layers" Button and add one of the Layers
5. Select the added Layer and click the button again and choose "Replace Layer"
6. In the Opened Object Picker double click the other Layer
7. In Scene View click on the created Terrain
8. Observe the Terrain Layers List

Actual results: After replacing the initial Terrain Layer and then clicking the Terrain for which the Terrain Layer was replaced, the Initial Terrain Layer is added to the Terrain Layer List, the replaced Terrain Settings are still visible in the Inspector

Expected results: When Replacing Terrain in the Terrain Layer List, new Layer is used for Painting Texture and it's settings are shown in the Inspector

Reproducible with versions: 6000.0.68f1, 6000.3.9f1, 6000.4.0b9, 6000.5.0a7

Tested on (OS): Windows 11