LU-8753 llog: remove lgh_write_offset

LU-8753 llog: remove lgh_write_offset

Remove lgh_write_offset for remote llog object,
since it is not easy to be refreshed when remote
transaction fails, which might cause llog file
corruption. Instead let's rely on the osp object
cache to invalidate and update the llog object
size.

Signed-off-by: Di Wang <di.wang@intel.com>
Change-Id: I38aa9ce2c5ac6485bf0cf6be023b8edde986b5d3
Reviewed-on: https://review.whamcloud.com/24008
Tested-by: Jenkins
Tested-by: Maloo <hpdd-maloo@intel.com>
Reviewed-by: Fan Yong <fan.yong@intel.com>
Reviewed-by: Lai Siyao <lai.siyao@intel.com>
Reviewed-by: Oleg Drokin <oleg.drokin@intel.com>