You don't need to (1) and (2) any more, it's now optional.
However, the build-in Ed25519 implementation is still a bit slower than the plugin, so it might make sense to keep using the plugin for now, in particular on legacy platforms. Alternatively, try turning off the plugin by commenting out the AsymmetricKeyAlgorithm.Register
call, and see whether performance is affected in your scenarios before deciding whether to remove the plugin.