simplify parity machine (#10469)

* simplify ethcore machine by removing redundant traits

* further ethereum machine simplifications

* removed obsolete todo

ethcore/src/machine/mod.rs

@@ -0,0 +1,7 @@
+//! Generalization of a state machine for a consensus engine.
+
+mod impls;
+mod traits;
+
+pub use self::impls::*;
+pub use self::traits::*;