User has the option to Delete a Context Block inside the Master Stack which leaves a selection highlight

Steps to reproduce:

1. Create or open a Project with the Shader Graph installed
2. Create or open a Shader Graph
3. Select either the Vertex or Fragment Context
4. Right click and select "Delete"

Actual results: Context is not deleted, a light blue selection highlight is left on the Context, the User is then able to try and delete the other Context and the blue selection highlight appears on it as well

Expected results: If the Contexts inside the Master Stack are not supposed to be deleted, the option should not be exposed to Users

Reproducible with versions: 2021.3.41f1, 2022.3.38f1, 6000.0.12f1

Tested on (OS): Windows 10/11