fix: remove server unimplemented GrpcStorageImpl#getServiceAccount (#2718)

Partial revert of 96b6330

Author: BenWhitehead

google-cloud-storage/src/main/java/com/google/cloud/storage/GrpcStorageImpl.java

@@ -26,7 +26,6 @@
 import static com.google.cloud.storage.StorageV2ProtoUtils.objectAclEntityOrAltEq;
 import static com.google.cloud.storage.Utils.bucketNameCodec;
 import static com.google.cloud.storage.Utils.ifNonNull;
-import static com.google.cloud.storage.Utils.projectNameCodec;
 import static com.google.common.base.MoreObjects.firstNonNull;
 import static java.util.Objects.requireNonNull;
 
@@ -90,7 +89,6 @@
 import com.google.storage.v2.GetBucketRequest;
 import com.google.storage.v2.GetNotificationConfigRequest;
 import com.google.storage.v2.GetObjectRequest;
-import com.google.storage.v2.GetServiceAccountRequest;
 import com.google.storage.v2.ListBucketsRequest;
 import com.google.storage.v2.ListNotificationConfigsRequest;
 import com.google.storage.v2.ListNotificationConfigsResponse;
@@ -1390,16 +1388,7 @@ public List<Boolean> testIamPermissions(
 
  @Override
  public ServiceAccount getServiceAccount(String projectId) {
- GetServiceAccountRequest req =
- GetServiceAccountRequest.newBuilder()
- .setProject(projectNameCodec.encode(projectId))
- .build();
- GrpcCallContext retryContext = Retrying.newCallContext();
- return Retrying.run(
- getOptions(),
- retryAlgorithmManager.getFor(req),
- () -> storageClient.getServiceAccountCallable().call(req, retryContext),
- codecs.serviceAccount());
+ return CrossTransportUtils.throwHttpJsonOnly(Storage.class, "getServiceAccount");
  }
 
  @Override

google-cloud-storage/src/main/java/com/google/cloud/storage/Storage.java

@@ -4781,7 +4781,7 @@ List<Boolean> testIamPermissions(
  * @return the service account associated with this project
  * @throws StorageException upon failure
  */
- @TransportCompatibility({Transport.HTTP, Transport.GRPC})
+ @TransportCompatibility({Transport.HTTP})
  ServiceAccount getServiceAccount(String projectId);
 
  /**

google-cloud-storage/src/test/java/com/google/cloud/storage/conformance/retry/RpcMethodMappings.java

@@ -2114,6 +2114,7 @@ static final class ServiceAccount {
  private static void get(ArrayList<RpcMethodMapping> a) {
  a.add(
  RpcMethodMapping.newBuilder(59, serviceaccount.get)
+ .withApplicable(TestRetryConformance.transportIs(Transport.HTTP))
  .withTest(
  (ctx, c) ->
  ctx.map(

google-cloud-storage/src/test/java/com/google/cloud/storage/it/ITServiceAccountTest.java

@@ -32,7 +32,7 @@
 @RunWith(StorageITRunner.class)
 @CrossRun(
  backends = {Backend.PROD},
- transports = {Transport.HTTP, Transport.GRPC})
+ transports = {Transport.HTTP})
 public class ITServiceAccountTest {
 
  private static final String SERVICE_ACCOUNT_EMAIL_SUFFIX =