Remove a compile warning introduced in r12688.
Remove a compile warning introduced in r12688.

* subversion/libsvn_client/export.c
  (svn_client_export3): Remove unused variable.

jmckaskill/subversion,jmckaskill/subversion,jmckaskill/subversion,jmckaskill/subversion,jmckaskill/subversion,jmckaskill/subversion,jmckaskill/subversion,jmckaskill/subversion