Remove module-level allows

Now that this codebase is more mature, remove allow directives so that
if we introduce issues, the compiler will tell us.

Bug: none
Test: compiles
Test: keystore2_test
Change-Id: If24b4ea40e0e2e1368e575e1e0bf6004bb318a42
diff --git a/keystore2/src/legacy_blob.rs b/keystore2/src/legacy_blob.rs
index 423f507..7c8a909 100644
--- a/keystore2/src/legacy_blob.rs
+++ b/keystore2/src/legacy_blob.rs
@@ -12,8 +12,6 @@
 // See the License for the specific language governing permissions and
 // limitations under the License.
 
-#![allow(dead_code)]
-
 //! This module implements methods to load legacy keystore key blob files.
 
 use crate::{
@@ -227,7 +225,7 @@
     const LENGTH_OFFSET: usize = 4 + Self::IV_SIZE + Self::GCM_TAG_LENGTH;
     const IV_OFFSET: usize = 4;
     const AEAD_TAG_OFFSET: usize = Self::IV_OFFSET + Self::IV_SIZE;
-    const DIGEST_OFFSET: usize = Self::IV_OFFSET + Self::IV_SIZE;
+    const _DIGEST_OFFSET: usize = Self::IV_OFFSET + Self::IV_SIZE;
 
     /// Construct a new LegacyBlobLoader with a root path of `path` relative to which it will
     /// expect legacy key blob files.