Remove the (currently) final deprecation warning from JavaHL.

* subversion/bindings/javahl/native/org_apache_subversion_javahl_util_DiffLib.cpp
  (Java_org_apache_subversion_javahl_util_DiffLib_nativeFileMerge):
   Use svn_diff_file_output_merge3.


git-svn-id: https://svn.apache.org/repos/asf/subversion/trunk@1618907 13f79535-47bb-0310-9956-ffa450edef68