Remove some unused parameters.

* subversion/libsvn_fs_x/transaction.c
  (get_final_id): Drop the unused START_ID and FORMAT parameters.
  (write_final_rev): Update caller and make it lose its START_NODE_ID
                     and START_COPY_ID parameters.
  (commit_body): Update caller and remove respective local variables.

git-svn-id: https://svn.apache.org/repos/asf/subversion/trunk@1568688 13f79535-47bb-0310-9956-ffa450edef68