fix: remove needless use of itertools (#11029)

* Remove needless use of `itertools` in `ethcore-light`
* Replace `itertools::repeat::call` with `std::iter::repeat_with`

ethcore/engines/authority-round/src/lib.rs

@@ -1506,7 +1506,7 @@ impl Engine for AuthorityRound {
 
 		let mut hash = *chain_head.parent_hash();
 
-		let mut ancestry = itertools::repeat_call(move || {
+		let mut ancestry = std::iter::repeat_with(move || {
 			chain(hash).and_then(|header| {
 				if header.number() == 0 { return None }
 				hash = *header.parent_hash();
@@ -1548,7 +1548,7 @@ impl Engine for AuthorityRound {
 				// to construct transition proof. author == ec_recover(sig) known
 				// since the blocks are in the DB.
 				let mut hash = chain_head.hash();
-				let mut finality_proof: Vec<_> = itertools::repeat_call(move || {
+				let mut finality_proof: Vec<_> = std::iter::repeat_with(move || {
 					chain(hash).and_then(|header| {
 						hash = *header.parent_hash();
 						if header.number() == 0 { None }

ethcore/light/Cargo.toml

@@ -34,7 +34,6 @@ rlp_derive = { path = "../../util/rlp-derive" }
 smallvec = "0.6"
 futures = "0.1"
 rand = "0.6"
-itertools = "0.5"
 bincode = "1.1"
 serde = "1.0"
 serde_derive = "1.0"

ethcore/light/src/client/header_chain.rs

@@ -550,7 +550,7 @@ impl HeaderChain {
 						let canon = &era_entry.candidates[0];
 						(canon.hash, canon.total_difficulty)
 					};
-					cht::compute_root(cht_num, ::itertools::repeat_call(iter))
+					cht::compute_root(cht_num, std::iter::repeat_with(iter))
 						.expect("fails only when too few items; this is checked; qed")
 				};
 

ethcore/light/src/lib.rs

@@ -67,11 +67,9 @@ extern crate ethereum_types;
 extern crate ethcore_miner as miner;
 extern crate hash_db;
 extern crate parity_util_mem;
-extern crate parity_util_mem as mem;
 extern crate parity_util_mem as malloc_size_of;
 extern crate failsafe;
 extern crate futures;
-extern crate itertools;
 extern crate keccak_hasher;
 extern crate machine;
 extern crate memory_db;