Remove an unused argument from a static function.

* subversion/libsvn_diff/diff_file.c
  (read_chunk): Remove unused path argument.

  (increment_chunk,
   decrement_chunk,
   find_identical_suffix,
   datasources_open,
   datasource_get_next_token,
   token_compare): Update caller.


git-svn-id: https://svn.apache.org/repos/asf/subversion/trunk@1607070 13f79535-47bb-0310-9956-ffa450edef68