Revert "[cobalt] Enable encryption to the shuffler."

This reverts commit 81345fa6.

Reason for revert: There is evidence decryption is failing in the backend.

Original change's description:
> [cobalt] Enable encryption to the shuffler.
> 
> testing=manual
> 
> Change-Id: I1f68574278249f879fce7b2bb8fb6325f6f75b8a

TBR=azani@google.com,pesk@google.com

Change-Id: I3d12510f82065f8999c8c0a68eb87b26a881a94c
No-Presubmit: true
No-Tree-Checks: true
No-Try: true

src/cobalt/bin/app/cobalt_app.cc

@@ -41,7 +41,6 @@ constexpr char kAnalyzerPublicKeyPemPath[] =
 constexpr char kShufflerPublicKeyPemPath[] =
     "/pkg/data/certs/cobaltv0.1/shuffler_public.pem";
 constexpr char kAnalyzerTinkPublicKeyPath[] = "/pkg/data/keys/analyzer_public";
-constexpr char kShufflerTinkPublicKeyPath[] = "/pkg/data/keys/shuffler_public";
 constexpr char kMetricsRegistryPath[] = "/pkg/data/global_metrics_registry.pb";
 
 constexpr char kLegacyObservationStorePath[] = "/data/legacy_observation_store";
@@ -88,9 +87,8 @@ CobaltApp::CobaltApp(async_dispatcher_t* dispatcher,
       encrypt_to_analyzer_(util::EncryptedMessageMaker::MakeHybridTink(
                                ReadPublicKeyPem(kAnalyzerTinkPublicKeyPath))
                                .ValueOrDie()),
-      encrypt_to_shuffler_(util::EncryptedMessageMaker::MakeHybridTink(
-                               ReadPublicKeyPem(kShufflerTinkPublicKeyPath))
-                               .ValueOrDie()),
+      // TODO(azani): Support encryption to the shuffler.
+      encrypt_to_shuffler_(util::EncryptedMessageMaker::MakeUnencrypted()),
 
       legacy_shipping_manager_(
           UploadScheduler(target_interval, min_interval, initial_interval),