How to reproduce:
1. Open user's attached project (unity_delete_world.zip)
2. Enter Play mode

Expected result: Created worlds are successfully disposed
Actual result: Constant InvalidOperationException spam when calling the Destroy() method

Reproducible with: 2019.3.2f1, 2020.1.0a23 (with all package versions)
Unity Netcode package was introduced in 2019.3

Three types of errors include these:
InvalidOperationException: Unity.NetCode.ClientPresentationSystemGroup has already been destroyed. It may not be used anymore.
InvalidOperationException: Unity.NetCode.ClientInitializationSystemGroup has already been destroyed. It may not be used anymore.
InvalidOperationException: Unity.NetCode.ClientSimulationSystemGroup has already been destroyed. It may not be used anymore.

Notes:
- The Destroy() method in the attached project goes through all previously created worlds and disposes them
- Latest Unity Netcode package depends on at least Entities preview.4 - 0.3.0, tests were done on Entities preview.17 - 0.5.0