Update remaining references to the deprecated svn_ra_do_update2() to refer
to svn_ra_do_update3() instead.  A follow-up to r1465292.

* subversion/include/svn_ra_svn.h
  (svn_ra_svn_write_cmd_update): Update a cross-reference in the doc string.
  (svn_ra_svn_write_cmd_switch): The same for switch, which was deprecated
    in an earlier commit.

* tools/client-side/svn-bench/null-export-cmd.c
  (bench_null_export): s/svn_ra_do_update2/svn_ra_do_update3/.


git-svn-id: https://svn.apache.org/repos/asf/subversion/trunk@1465298 13f79535-47bb-0310-9956-ffa450edef68