Delete layers that are referenced by other datasets

[normanrz]

Context

Symlinks are used to reuse layers in new datasets. When the original dataset is deleted from within wk, these symlinks are broken, making the new datasets broken.

Expected Behavior

When a dataset is deleted that has layers that other datasets reference via symlinks, these layers should be moved to another dataset and the symlinks repaired. I think it is fine to restrict the symlink search to an organization.

[fm3]

related: #6726