Fix method signatures in JavaHL's AuthnCallback.

[in subversion/bindings/javahl]
* native/AuthnCallback.cpp
  (::JavaHL::AuthnCallback::static_init): Fix invalid method signatures.


git-svn-id: https://svn.apache.org/repos/asf/subversion/trunk@1599258 13f79535-47bb-0310-9956-ffa450edef68