Eliminate ineffective code from dag_clone_child and simplify callers
in FSFS and FSX.  BDB uses different code.

* subversion/libsvn_fs_fs/dag.h
  (svn_fs_fs__dag_clone_child): drop is_parent_copyroot parameter

* subversion/libsvn_fs_x/dag.h
  (svn_fs_x__dag_clone_child): ditto

* subversion/libsvn_fs_fs/dag.c
  (svn_fs_fs__dag_clone_child): remove the ineffective copy-from assignment

* subversion/libsvn_fs_x/dag.c
  (svn_fs_x__dag_clone_child): ditto

* subversion/libsvn_fs_fs/tree.c
  (make_path_mutable): update & simplify caller

* subversion/libsvn_fs_x/tree.c
  (make_path_mutable): ditto

Found by: rassilon

git-svn-id: https://svn.apache.org/repos/asf/subversion/trunk@1527344 13f79535-47bb-0310-9956-ffa450edef68