Derive default for State (#2616)

There is no need for a manual implementation of `Default` for `State`.
It existing is distracting, hence it is removed.

src/internet_identity/src/state.rs

@@ -156,11 +156,14 @@ pub struct RateLimitState {
     pub token_timestamp: Timestamp,
 }
 
+#[derive(Default)]
 enum StorageState {
+    #[default]
     Uninitialised,
     Initialised(Storage<DefaultMemoryImpl>),
 }
 
+#[derive(Default)]
 struct State {
     storage_state: RefCell<StorageState>,
     sigs: RefCell<SignatureMap>,
@@ -188,24 +191,6 @@ struct State {
     event_data_uniqueness_counter: Cell<u16>,
 }
 
-impl Default for State {
-    fn default() -> Self {
-        Self {
-            storage_state: RefCell::new(StorageState::Uninitialised),
-            sigs: RefCell::new(SignatureMap::default()),
-            temp_keys: RefCell::new(TempKeys::default()),
-            last_upgrade_timestamp: Cell::new(0),
-            inflight_challenges: RefCell::new(HashMap::new()),
-            tentative_device_registrations: RefCell::new(HashMap::new()),
-            usage_metrics: RefCell::new(UsageMetrics::default()),
-            persistent_state: RefCell::new(PersistentState::default()),
-            archive_status_cache: RefCell::new(None),
-            registration_rate_limit: RefCell::new(None),
-            event_data_uniqueness_counter: Cell::new(0),
-        }
-    }
-}
-
 // Checks if salt is empty and calls `init_salt` to set it.
 pub async fn ensure_salt_set() {
     let salt = storage_borrow(|storage| storage.salt().cloned());