Replace local block size constants from the FSFS stats code and use
the FS provided info instead.

* subversion/libsvn_fs_fs/stats.c
  (REV_FILE_BLOCK_SIZE,
   INDEX_BLOCK_SIZE): Remove these constants.
  (read_item): Use the block size provided by the REV_FILE object.
  (read_log_rev_or_packfile): Take the block size from the FS settings.

git-svn-id: https://svn.apache.org/repos/asf/subversion/trunk@1632853 13f79535-47bb-0310-9956-ffa450edef68