We'll just need the deprecation warning in 2.99.  In 3.0 it's totally fine the pass `--seed` alone -- that's a big point of this feature, right?

Also, I don't think the `unless` conditional here is sufficient: the user could be setting the order to random via an `RSpec.configure` block`, and then assigning the seed at the command line, and that's totally sufficient, w/ no warning needed.