install: Drop unneeded sha2 dependency (#7108)

* Poll for updates slower

* Drop sha2 dependency

install/src/update_manifest.rs

@@ -1,17 +1,18 @@
 use serde_derive::{Deserialize, Serialize};
 use solana_config_program::ConfigState;
-use solana_sdk::pubkey::Pubkey;
-use solana_sdk::signature::{Signable, Signature};
-use std::borrow::Cow;
-use std::error;
-use std::io;
+use solana_sdk::{
+    hash::Hash,
+    pubkey::Pubkey,
+    signature::{Signable, Signature},
+};
+use std::{borrow::Cow, error, io};
 
 /// Information required to download and apply a given update
 #[derive(Serialize, Deserialize, Default, Debug, PartialEq)]
 pub struct UpdateManifest {
     pub timestamp_secs: u64, // When the release was deployed in seconds since UNIX EPOCH
     pub download_url: String, // Download URL to the release tar.bz2
-    pub download_sha256: String, // SHA256 digest of the release tar.bz2 file
+    pub download_sha256: Hash, // SHA256 digest of the release tar.bz2 file
 }
 
 /// Userdata of an Update Manifest program Account.