Complete the conversion of the file callbacks in the merge processing to the
diff tree processor (aka the easiest part).

* subversion/libsvn_client/merge.c
  (merge_file_deleted): Implement svn_diff_tree_processor_t api.
  (ignore_file_deleted): New stub.
  (merge_callbacks): Use stub.
  (do_merge): Tweak spacing. Use merge_file_deleted.


git-svn-id: https://svn.apache.org/repos/asf/subversion/trunk@1440486 13f79535-47bb-0310-9956-ffa450edef68