Remove relations from DTOs

[DannySS123]

The relations are defined in the prisma.schema file, so we don't usually need them in the DTOs.
If there was an endpoint, that would return more things, for that we could create a DTO containing other fields as well.
But for now, let's just remove all fields from the DTOs (every entity.ts) that represent relations. (Like: ownedEvents: Event[] in the User DTO)