Fix a "will not be inlined" warning.

* subversion/libsvn_fs_fs/tree.c
  (stringify_node): Drop the inline marker since this function will
                    onlx be called for error object creation.

git-svn-id: https://svn.apache.org/repos/asf/subversion/trunk@1555492 13f79535-47bb-0310-9956-ffa450edef68