In the libsvn_client diff code: Optimize the resolving of peg revisions a bit
by doing more things at once.

* subversion/libsvn_client/diff.c
  (resolve_pegged_diff_target_url): Remove function.
  (diff_prepare_repos_repos): Resolve paths and revisions in one step.


git-svn-id: https://svn.apache.org/repos/asf/subversion/trunk@1570205 13f79535-47bb-0310-9956-ffa450edef68