NativeSecp256k1: deprecate native interface to libsecp256k1

This native implementation is unmaintained and untested for years.

core/src/main/java/org/bitcoin/NativeSecp256k1.java

@@ -39,7 +39,9 @@ import static org.bitcoin.NativeSecp256k1Util.assertEquals;
  * and `make` then copy `.libs/libsecp256k1.so` to your system library path
  * or point the JVM to the folder containing it with -Djava.library.path
  * </p>
+ * @deprecated See https://github.com/bitcoinj/bitcoinj/issues/2267
  */
+@Deprecated
 public class NativeSecp256k1 {
 
     private static final ReentrantReadWriteLock rwl = new ReentrantReadWriteLock();

core/src/main/java/org/bitcoin/NativeSecp256k1Util.java

@@ -21,7 +21,9 @@ import org.slf4j.LoggerFactory;
 
 /**
  * Assertion utilities for {@link NativeSecp256k1}
+ * @deprecated See https://github.com/bitcoinj/bitcoinj/issues/2267
  */
+@Deprecated
 public class NativeSecp256k1Util {
 
     private static final Logger log = LoggerFactory.getLogger(NativeSecp256k1Util.class);

core/src/main/java/org/bitcoin/Secp256k1Context.java

@@ -21,7 +21,9 @@ import org.slf4j.LoggerFactory;
 
 /**
  * This class holds the context reference used in native methods to handle ECDSA operations.
+ * @deprecated See https://github.com/bitcoinj/bitcoinj/issues/2267
  */
+@Deprecated
 public class Secp256k1Context {
 
     private static final boolean enabled; // true if the library is loaded