Remove some unneeded baton variables in serf. No functional changes.

* subversion/libsvn_ra_serf/options.c
  (options_context_t): Remove unneeded variable.
  (create_options_req): Update setter.

* subversion/libsvn_ra_serf/update.c
  (fetch_ctx_t): Keep boolean instead of two baton pointers.
  (report_context_t): Remove connection variable.
  (headers_fetch): Update user.
  (fetch_for_file): Update setter.
  (make_update_reporter): Update setter.


git-svn-id: https://svn.apache.org/repos/asf/subversion/trunk@1557567 13f79535-47bb-0310-9956-ffa450edef68