Remove desktop support for Ropsten, Rinkeby, and Kovan test networks and add Sepolia

[nvonpentz]

as they are being deprecated by our RPC provider October 5th.

[nvonpentz]

I will also add Sepolia in this change because some tests depend there being two different Ethereum testnets. This way I can swap those with Sepolia and Goerli without having to modify the core test logic.