Move srml RPC extensions to separate crates (#3791)

* Move srml-system RPC out.

* Fix tests for system-rpc module.

* Contracts RPC moved.

* Fix rpc test.

* Clean up.

* Update lockfile.

* Bump runtime version.

* Update srml/contracts/rpc/runtime-api/src/lib.rs

Co-Authored-By: Bastian Köcher <bkchr@users.noreply.github.com>

* Bump impl version.

substrate/srml/system/rpc/runtime-api/Cargo.toml

@@ -0,0 +1,16 @@
+[package]
+name = "srml-system-rpc-runtime-api"
+version = "2.0.0"
+authors = ["Parity Technologies <admin@parity.io>"]
+edition = "2018"
+
+[dependencies]
+client = { package = "substrate-client", path = "../../../../core/client", default-features = false }
+codec = { package = "parity-scale-codec", version = "1.0.0", default-features = false  }
+
+[features]
+default = ["std"]
+std = [
+	"client/std",
+	"codec/std",
+]

substrate/srml/system/rpc/runtime-api/src/lib.rs

@@ -0,0 +1,34 @@
+// Copyright 2019 Parity Technologies (UK) Ltd.
+// This file is part of Substrate.
+
+// Substrate is free software: you can redistribute it and/or modify
+// it under the terms of the GNU General Public License as published by
+// the Free Software Foundation, either version 3 of the License, or
+// (at your option) any later version.
+
+// Substrate is distributed in the hope that it will be useful,
+// but WITHOUT ANY WARRANTY; without even the implied warranty of
+// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+// GNU General Public License for more details.
+
+// You should have received a copy of the GNU General Public License
+// along with Substrate.  If not, see <http://www.gnu.org/licenses/>.
+
+//! Runtime API definition required by System RPC extensions.
+//!
+//! This API should be imported and implemented by the runtime,
+//! of a node that wants to use the custom RPC extension
+//! adding System access methods.
+
+#![cfg_attr(not(feature = "std"), no_std)]
+
+client::decl_runtime_apis! {
+	/// The API to query account nonce (aka transaction index).
+	pub trait AccountNonceApi<AccountId, Index> where
+		AccountId: codec::Codec,
+		Index: codec::Codec,
+	{
+		/// Get current account nonce of given `AccountId`.
+		fn account_nonce(account: AccountId) -> Index;
+	}
+}