On the fsfs-format7 branch: docstring-only fix

* subversion/libsvn_fs_fs/string_table.h
  (svn_fs_fs__serialize_string_table,
   svn_fs_fs__deserialize_string_table): correct docstrings


git-svn-id: https://svn.apache.org/repos/asf/subversion/branches/fsfs-format7@1476640 13f79535-47bb-0310-9956-ffa450edef68