build: remove rococo-native from the build (#141)

Closes #139

I've verified that rococo-runtime is not built. However,
rococo-runtime-constants
are still built. Running `cargo tree` confirms the observation,
`rococo-runtime` is
not in tree and `rococo-runtime-constants` is.

The changes of Cargo.lock are a bit confusing though, because it's
actually the opposite:
-constants is removed and rococo-runtime still is present.

I've also verified that the sovereign demo works.

Author: pepyakin

Cargo.lock

@@ -59,7 +59,7 @@ substrate-prometheus-endpoint = { git = "https://github.com/paritytech/polkadot-
 try-runtime-cli = { git = "https://github.com/paritytech/polkadot-sdk", optional = true , branch = "release-polkadot-v1.4.0" }
 
 # Polkadot
-polkadot-cli = { git = "https://github.com/paritytech/polkadot-sdk", features = ["rococo-native"] , branch = "release-polkadot-v1.4.0" }
+polkadot-cli = { git = "https://github.com/paritytech/polkadot-sdk", branch = "release-polkadot-v1.4.0" }
 polkadot-primitives = { git = "https://github.com/paritytech/polkadot-sdk", branch = "release-polkadot-v1.4.0" }
 xcm = { package = "staging-xcm", git = "https://github.com/paritytech/polkadot-sdk", default-features = false, branch = "release-polkadot-v1.4.0" }