Simplify tests

[mtfishman]

We can remove all of the current tests and just test the constructors introduced in this package, i.e. just the functions exported in https://github.com/ITensor/ITensorGPU.jl/blob/main/src/ITensorGPU.jl. In terms of functionality, we can rely on the NDTensors.jl and ITensors.jl which test GPU functionality more systematically.