Revert "NetworkIdentity.observers dictionary is always created, but always empty on clients. Gets rid of all null checks." to fix server-only bug not allowing movement on client, e.g. in uMMORPG (f56507f)
Revert "refactor: consolidate prefab and spawn handlers (#817)" to fix a bug where if editor=host, build=client, we receive scene object not found when walking out of and back into an observer's range (1f07af0)