remove the di_version icdicone field v2

[Christoph Hellwig <hch@xxxxxx>]

Hi all,

this series remove the not really needed ic_version field from
the icdinode structure.

Changes since v1:
 - split into multiple patches
 - add a new xfs_sb_version_has_large_dinode helper instead of using
   xfs_sb_version_hascrc
 - add a comment about the relationship of file system and dinode
   versions
 - add a few more trivial cleanups