chore: Make extractStatus method package-private

Author: lqiu96

java-datastore/google-cloud-datastore/src/main/java/com/google/cloud/datastore/DatastoreException.java

@@ -176,7 +176,7 @@ static DatastoreException propagateUserException(Exception ex) {
    * @param throwable the throwable to extract the status code from
    * @return the status code name, or "UNKNOWN" if not determinable
    */
-  public static String extractStatusCode(Throwable throwable) {
+  static String extractStatusCode(Throwable throwable) {
     Throwable current = throwable;
     while (current != null) {
       if (current instanceof DatastoreException) {