Remove a dead initialization, followup to r1478220.

* subversion/libsvn_client/log.c
  (run_ra_get_log): Move segment_url into the only block it is used and remove
    an initialization that never gets used.


git-svn-id: https://svn.apache.org/repos/asf/subversion/trunk@1478465 13f79535-47bb-0310-9956-ffa450edef68