Follow-up to r1597989: Remove now unnecessary code complexity.

* subversion/libsvn_fs_fs/tree.c
  (copy_type_t): Remove.
  (copy_helper): Replace COPY_TYPE enum argument with boolean 
   PRESERVE_HISTORY.
  (fs_copy, fs_revision_link): Update callers.


git-svn-id: https://svn.apache.org/repos/asf/subversion/trunk@1601633 13f79535-47bb-0310-9956-ffa450edef68