Revert "Create bank snapshots (#3671)" (#4243)

This reverts commit abf2b300da.

core/tests/crds_gossip.rs

@@ -1,4 +1,5 @@
 use bincode::serialized_size;
+use hashbrown::HashMap;
 use log::*;
 use rayon::prelude::*;
 use solana::contact_info::ContactInfo;
@@ -10,7 +11,6 @@ use solana::crds_value::CrdsValueLabel;
 use solana_sdk::hash::hash;
 use solana_sdk::pubkey::Pubkey;
 use solana_sdk::timing::timestamp;
-use std::collections::HashMap;
 use std::sync::{Arc, Mutex};
 
 type Node = Arc<Mutex<CrdsGossip>>;