Remove Polkadot & Kusama native runtime (#1304)

This pull request removes the Polkadot and Kusama native runtime from
the polkadot node. This brings some implications with it:

There are no more kusama/polkadot-dev chain specs available. We will
need to write some tooling in the fellowship repo to provide them
easily.

The try-runtime job for polkadot & kusama is not available anymore as we
don't have the dev chain specs anymore.

Certain benchmarking commands will also not work until we migrate them
to use a runtime api.

Some crates in utils are still depending on the polkadot/kusama native
runtime that will also need to be fixed.

Port of: https://github.com/paritytech/polkadot/pull/7467

polkadot/cli/src/error.rs

@@ -58,3 +58,9 @@ pub enum Error {
 	#[error("This subcommand is only available when compiled with `{feature}`")]
 	FeatureNotEnabled { feature: &'static str },
 }
+
+impl From<String> for Error {
+	fn from(s: String) -> Self {
+		Self::Other(s)
+	}
+}