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",
+]