Remove unused imports/ doc comments. (#2276)

* Remove unused imports/ doc comments

* Better doc for node template.

substrate/core/network/src/consensus_gossip.rs

@@ -416,7 +416,6 @@ impl<B: BlockT> ConsensusGossip<B> {
 
 		if let Some((topic, keep)) = validation_result {
 			if let Some(ref mut peer) = self.peers.get_mut(&who) {
-				use std::collections::hash_map::Entry;
 				peer.known_messages.insert(message_hash);
 				if let Entry::Occupied(mut entry) = self.live_message_sinks.entry((engine_id, topic)) {
 					debug!(target: "gossip", "Pushing consensus message to sinks for {}.", topic);

substrate/core/network/src/message.rs

@@ -66,7 +66,7 @@ pub type BlockResponse<B> = generic::BlockResponse<
 /// A set of transactions.
 pub type Transactions<E> = Vec<E>;
 
-/// Bits of block data and associated artifacts to request.
+// Bits of block data and associated artifacts to request.
 bitflags! {
 	/// Node roles bitmask.
 	pub struct BlockAttributes: u8 {

substrate/core/network/src/test/sync.rs

@@ -19,8 +19,6 @@ use client::blockchain::HeaderBackend as BlockchainHeaderBackend;
 use crate::config::Roles;
 use consensus::BlockOrigin;
 use std::collections::HashSet;
-use std::thread;
-use std::time::Duration;
 use super::*;
 
 fn test_ancestor_search_when_common_is(n: usize) {