Boot hashbrown (#5505)

As of Rust 1.36.0, hashbrown now implements the HashMap in std (which
implements HashSet).

https://blog.rust-lang.org/2019/07/04/Rust-1.36.0.html#a-new-hashmapk,-v%3E-implementation

runtime/Cargo.toml

@@ -14,7 +14,6 @@ bv = { version = "0.11.0", features = ["serde"] }
 byteorder = "1.3.2"
 fnv = "1.0.6"
 fs_extra = "1.1.0"
-hashbrown = "0.5.0"
 lazy_static = "1.3.0"
 libc = "0.2.61"
 libloading = "0.5.2"

runtime/benches/bloom.rs

@@ -6,8 +6,7 @@ use fnv::FnvHasher;
 use solana_runtime::bloom::{Bloom, BloomHashIndex};
 use solana_sdk::hash::{hash, Hash};
 use solana_sdk::signature::Signature;
-//use std::collections::HashSet;
-use hashbrown::HashSet;
+use std::collections::HashSet;
 use std::hash::Hasher;
 use test::Bencher;
 

runtime/src/accounts_index.rs

@@ -7,7 +7,7 @@ type ForkList<T> = Vec<(Fork, T)>;
 
 #[derive(Debug, Default)]
 pub struct AccountsIndex<T> {
-    pub account_maps: hashbrown::HashMap<Pubkey, RwLock<ForkList<T>>>,
+    pub account_maps: HashMap<Pubkey, RwLock<ForkList<T>>>,
 
     pub roots: HashSet<Fork>,