Remove the ability to download service account credentials

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

java/google/registry/keyring/api/Keyring.java

@@ -151,15 +151,6 @@ public interface Keyring extends AutoCloseable {
    */
   String getJsonCredential();
 
-  /**
-   * Returns the encrypted data for the given key name. Only use this method when decryption is not
-   * required.
-   */
-  String getEncryptedData(String keyName);
-
-  /** Decrypts the given encrypted data using the key name. */
-  byte[] getDecryptedData(String keyName, String encryptedData);
-
   // Don't throw so try-with-resources works better.
   @Override
   void close();