complete null-signatures removal (#11491)

* complete null-signatures removal

* unsigned transactions are disallowed by the type system

* "fix" verification test

* machine: bring the test back

* machine: simplify the test

ethcore/vm/src/schedule.rs

@@ -136,8 +136,6 @@ pub struct Schedule {
 	pub eip1283: bool,
 	/// Enable EIP-1706 rules
 	pub eip1706: bool,
-	/// VM execution does not increase null signed address nonce if this field is true.
-	pub keep_unsigned_nonce: bool,
 	/// Latest VM version for contract creation transaction.
 	pub latest_version: U256,
 	/// All supported non-legacy VM versions.
@@ -279,7 +277,6 @@ impl Schedule {
 			kill_dust: CleanDustMode::Off,
 			eip1283: false,
 			eip1706: false,
-			keep_unsigned_nonce: false,
 			latest_version: U256::zero(),
 			versions: HashMap::new(),
 			wasm: None,
@@ -371,7 +368,6 @@ impl Schedule {
 			kill_dust: CleanDustMode::Off,
 			eip1283: false,
 			eip1706: false,
-			keep_unsigned_nonce: false,
 			latest_version: U256::zero(),
 			versions: HashMap::new(),
 			wasm: None,