Empty contracts and structs require dummy fields in Move

[egroge]

If one were to write a contract or struct without any fields, like so:

contract MyContract {}

MyContract :: (any) {
  public init() {}

  public func one() -> Int {
    return 1
  }
}

then this will compile and work due to 011118f. However, the way that this works is just to insert a dummy variable into the underlying move struct if the contract is empty. This is not ideal. Ideally, we would not have a move struct for the contract at all if it is empty.