Removing instance of BlenderScene won't remove the scene assets.

[moonyuet]

Changelog Description

This PR is to fix the bug of removing BlenderScene instance also deleting the included asset inside it.
Resolve #61

Additional review information

n/a

Testing notes:

1. Create BlenderScene Instance with your assets
2. Removing it

[BigRoy]

I can see how and why this works - admittedly though, I feel like this does the exact opposite of what I expect would happen. I would instead expect the objects that are IN the instance to remain existing within the Blender scene and not ONLY live in the Blender Scene instance. It acts solely as an object set / container. Right?

[LiborBatek]

It partially resolve the issue and do not remove the objects/geometries once deleting publish instance blendScene but it is not removing also the Collection used for the publishing as seen on pic below:

so the instance is removed from the Publisher UI only and once refreshing it or creating new publish instance blendScene is leading to duplication and creation of another instance with 001 appendix. as seen below, which is undesirable.

We have to got rid of everything AVALON_INSTANCES related besides the actual scene objects aka user created content (e.g. models etc)

[BigRoy]

Didn't test - but code seems fine to me.

[LiborBatek]

Now all works as expected! All good...