Remove the ability to download service account credentials

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Created by MOE: https://github.com/google/moe
MOE_MIGRATED_REVID=224034254

java/google/registry/keyring/api/InMemoryKeyring.java

@@ -149,17 +149,6 @@ public final class InMemoryKeyring implements Keyring {
     return jsonCredential;
   }
 
-  @Override
-  public String getEncryptedData(String keyName) {
-    throw new RuntimeException(
-        "In-memory keyring does not support the retrieval of encrypted data.");
-  }
-
-  @Override
-  public byte[] getDecryptedData(String keyName, String encryptedData) {
-    throw new RuntimeException("In-memory keyring does not support decrypting of supplied data.");
-  }
-
   /** Does nothing. */
   @Override
   public void close() {}