Disable Disconnection of instance on the graph

Disable (and test) the call to _updateSuccessorList via SlapTool.updateComputerPartitionRelatedInstanceList.

Since the use of slapproxy forwarding requests on webrunner/theia, it created a broken state (internal instances start to fail).

This MR aims to disable the update and as well the garbage collection of the unlinked tree/graph since it wasn't widely used.

The expected feature (garbage collection/unrequested instance destructions) will be re-introduced properly after general review and fixes.