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

genesis_programs/src/lib.rs

@@ -35,7 +35,7 @@ pub fn get() -> Vec<(String, Pubkey)> {
 
 #[cfg(test)]
 mod tests {
-    use hashbrown::HashSet;
+    use std::collections::HashSet;
 
     #[test]
     fn test_id_uniqueness() {