Minor code consistency fix in FSFS: get rid of the redundant path_lock()
function and make the path to the pack lock file available through a
similar private API function.

* subversion/libsvn_fs_fs/util.h
  (svn_fs_fs__path_pack_lock): Declare this path constructor similarly to
                               the already existing one for the write lock.

* subversion/libsvn_fs_fs/util.c
  (svn_fs_fs__path_pack_lock): Moved here from fs_fs.c:path_pack_lock().

* subversion/libsvn_fs_fs/fs_fs.c
  (path_lock,
   path_pack_lock): Drop as redundant.
  (init_lock_baton,
   svn_fs_fs__create): Call the functions provide from utils.h
                       instead of the static ones.


git-svn-id: https://svn.apache.org/repos/asf/subversion/trunk@1588901 13f79535-47bb-0310-9956-ffa450edef68