impl Randomness trait for Babe and remove unused RandomBeacon trait (#4886)

* impl Randomness trait for Babe and remove unused RandomBeacon trait

* bump runtime version

substrate/bin/node/runtime/src/lib.rs

@@ -82,7 +82,7 @@ pub const VERSION: RuntimeVersion = RuntimeVersion {
 	// implementation changes and behavior does not, then leave spec_version as
 	// is and increment impl_version.
 	spec_version: 215,
-	impl_version: 1,
+	impl_version: 2,
 	apis: RUNTIME_API_VERSIONS,
 };