No Stadia support — fix for "can't add Editor script"

[neon-age]

This is a temp solution to avoid "can't add Editor script" error on MonoBehaviours.

Will be eventually fixed with re-organization and splitting assemblies into:

Assemblies
AV.Hierarchy.Core	Base folder, references Unity assemblies.
AV.Hierarchy.Runtime	MonoBehaviours, references Core.
AV.Hierarchy	Root, Editor-only, references Core and Runtime.

But it will introduce new conflicts, so firstly these dev branches need to be merged into master:

• hide-scene-visibility
• view-items-refactoring
• components-toolbar
• reorganization

Hope there is no developers that actually rely on Stadia 😅