There is no need to implement llog_cancel() as an llog operation. (We do not need to have a lop_cancel member in struct llog_operations. This method only used by changelogs now and the prototype is abused to make it work.

With lop_cancel removed, all uses of hsm_actions_logops, changelog_orig_logops, and osp_mds_ost_orig_logops can be replaces with llog_common_cat_ops.

LLOG_AGENT_ORIG_CTXT should be called LLOG_ACTIONS_ORIG_CTXT.

LLOG_AGENT_ORIG_CTXT setup and cleanup should be moved from the MDD layer to the MDT layer. Then there will be no need for the MDT to clone this context.