[BUG] "autoTilesKilledByOtherLayerUid" is not cleared in existing layers, after another layer was deleted.

[s-kania]

Hi. Steps to reproduce:

1. Create two layers, let it be X and Y.
2. In X layer, set autoTilesKilledByOtherLayerUid to Z layer.
3. Delete Z layer.
4. References in X layer, in property autoTilesKilledByOtherLayerUid to Z layer still exist, validation throws bugs, because this layer not exist anymore.