Refactors in advance of crypto-secure boot level

Various refactors that set the stage for a future change to make
max-boot-level keys cryptographically secure.

Bug: 176450483
Test: keystore2_test
Change-Id: I4e4e91ae23991131610c7a40f6d347ddcd528ac7
diff --git a/keystore2/src/legacy_blob.rs b/keystore2/src/legacy_blob.rs
index 7c8a909..c108b32 100644
--- a/keystore2/src/legacy_blob.rs
+++ b/keystore2/src/legacy_blob.rs
@@ -1285,7 +1285,7 @@
             CACERT_NON_AUTHBOUND,
         )?;
 
-        let key_manager = crate::super_key::SuperKeyManager::new();
+        let key_manager: SuperKeyManager = Default::default();
         let mut db = crate::database::KeystoreDB::new(temp_dir.path(), None)?;
         let legacy_blob_loader = LegacyBlobLoader::new(temp_dir.path());