Use parity-crypto updated to use upstream rust-secp256k1 (#11406)

* Use parity-crypto updated to use upstream rust-secp256k1

* Fetch dependency from git

* Missed a session ID

* Add free-standing inversion function that uses `libsecp256k1`

* fixed tests

* Update deps

* Use parity-crypto 0.5.0
Use libsecp256k1 0.3.5

* Review grumble

Co-authored-by: Svyatoslav Nikolsky <svyatonik@gmail.com>

ethcore/sync/src/block_sync.rs

@@ -671,7 +671,7 @@ mod tests {
 	}
 
 	fn dummy_signed_tx() -> SignedTransaction {
-		let keypair = Random.generate().unwrap();
+		let keypair = Random.generate();
 		Transaction::default().sign(keypair.secret(), None)
 	}