idsig: Migrate from ring to the openssl crate

Bug: 232676161
Test: atest libidsig.test
Change-Id: Icdda672a802e24f13ca071312d40bc1b44665155
diff --git a/libs/idsig/src/apksigv4.rs b/libs/idsig/src/apksigv4.rs
index a5578d8..3004ed1 100644
--- a/libs/idsig/src/apksigv4.rs
+++ b/libs/idsig/src/apksigv4.rs
@@ -175,7 +175,7 @@
 
         // Create hash tree (and root hash)
         let algorithm = match algorithm {
-            HashAlgorithm::SHA256 => &ring::digest::SHA256,
+            HashAlgorithm::SHA256 => openssl::hash::MessageDigest::sha256(),
         };
         let hash_tree = HashTree::from(&mut apk, size, salt, block_size, algorithm)?;