Revert "[apkverify] Skip DSA SHA256 during apk verification"

This reverts commit c68b95b84de4b852b0e6480df459b8f8ec8d41e3.

Reason for revert: b/248068872

Test: atest libidsig.test
Change-Id: Ib978f23954fe6d901b4806d230e3067c4572083f
diff --git a/libs/apkverify/src/algorithms.rs b/libs/apkverify/src/algorithms.rs
index ecca7ed..a1cf368 100644
--- a/libs/apkverify/src/algorithms.rs
+++ b/libs/apkverify/src/algorithms.rs
@@ -97,6 +97,14 @@
         &self,
         public_key: &'a PKey<pkey::Public>,
     ) -> Result<Verifier<'a>> {
+        ensure!(
+            !matches!(
+                self,
+                SignatureAlgorithmID::DsaWithSha256 | SignatureAlgorithmID::VerityDsaWithSha256
+            ),
+            "TODO(b/197052981): Algorithm '{:?}' is not implemented.",
+            self
+        );
         ensure!(public_key.id() == self.pkey_id(), "Public key has the wrong ID");
         let mut verifier = Verifier::new(self.new_message_digest(), public_key)?;
         if public_key.id() == pkey::Id::RSA {
@@ -122,14 +130,6 @@
         }
     }
 
-    /// DSA is not directly supported in openssl today. See b/197052981.
-    pub(crate) fn is_supported(&self) -> bool {
-        !matches!(
-            self,
-            SignatureAlgorithmID::DsaWithSha256 | SignatureAlgorithmID::VerityDsaWithSha256,
-        )
-    }
-
     fn pkey_id(&self) -> pkey::Id {
         match self {
             SignatureAlgorithmID::RsaPssWithSha256