Don't destroy subdocs on deletion from parent

Describe the bug I am building a Tree Provider, that supports relinking of items to other parents. While doing so, my child Docs get destroyed entirely, as soon as I delete them from the previous parent. If I get it right, it is happening through this line. I would expect/suggest to leave it up to the provider to destroy items during the 'subdocs' event.

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• This issue is a blocker for my project.