sc-cli: Remove SubstrateCli::native_runtime_version function (#14511)

The native runtime will be removed in the near future and thus this function will not be required
anymore.

\# Code changes

Downstream users just need to remove `native_runtime_version` from their implementation of the
`SubstrateCli` trait.

substrate/client/cli/src/lib.rs

@@ -248,6 +248,4 @@ pub trait SubstrateCli: Sized {
 		command.init(&Self::support_url(), &Self::impl_version(), logger_hook, &config)?;
 		Runner::new(config, tokio_runtime, signals)
 	}
-	/// Native runtime version.
-	fn native_runtime_version(chain_spec: &Box<dyn ChainSpec>) -> &'static RuntimeVersion;
 }