Remove concept of stateful transaction signers.

core/src/main/java/org/bitcoinj/signers/CustomTransactionSigner.java

@@ -40,7 +40,7 @@
  * some local API or something else.
  * </p>
  */
-public abstract class CustomTransactionSigner extends StatelessTransactionSigner {
+public abstract class CustomTransactionSigner implements TransactionSigner {
     private static final Logger log = LoggerFactory.getLogger(CustomTransactionSigner.class);
 
     @Override

core/src/main/java/org/bitcoinj/signers/LocalTransactionSigner.java

@@ -42,7 +42,7 @@
  * the same derivation path.</p>
  * <p>This signer always uses {@link Transaction.SigHash#ALL} signing mode.</p>
  */
-public class LocalTransactionSigner extends StatelessTransactionSigner {
+public class LocalTransactionSigner implements TransactionSigner {
     private static final Logger log = LoggerFactory.getLogger(LocalTransactionSigner.class);
 
     /**

core/src/main/java/org/bitcoinj/signers/MissingSigResolutionSigner.java

@@ -34,7 +34,7 @@
  * In MissingSigsMode.THROW mode this signer will throw an exception. It would be MissingSignatureException
  * for P2SH or MissingPrivateKeyException for other transaction types.
  */
-public class MissingSigResolutionSigner extends StatelessTransactionSigner {
+public class MissingSigResolutionSigner implements TransactionSigner {
     private static final Logger log = LoggerFactory.getLogger(MissingSigResolutionSigner.class);
 
     public Wallet.MissingSigsMode missingSigsMode = Wallet.MissingSigsMode.USE_DUMMY_SIG;

core/src/main/java/org/bitcoinj/signers/TransactionSigner.java

@@ -67,16 +67,6 @@ class MissingSignatureException extends RuntimeException {
      */
     boolean isReady();
 
-    /**
-     * Returns byte array of data representing state of this signer. It's used to serialize/deserialize this signer
-     */
-    byte[] serialize();
-
-    /**
-     * Uses given byte array of data to reconstruct internal state of this signer
-     */
-    void deserialize(byte[] data);
-
     /**
      * Signs given transaction's inputs.
      * Returns true if signer is compatible with given transaction (can do something meaningful with it).