Remove InherentsPool and introduce non-propagateable transactions. (#2695)

* Remove InherentsPool.

* Introduce transactions that are not propagated over the network.

* Bump spec version.

* Use separate flag for propagation.

* Fix tests.

substrate/core/transaction-pool/src/tests.rs

@@ -53,6 +53,7 @@ impl txpool::ChainApi for TestApi {
 			requires,
 			provides,
 			longevity: 64,
+			propagate: true,
 		})
 	}