MFC r312348: Remove writing 'residual' field of struct ctl_scsiio.

This field has no practical use and never readed. Initiators already
receive respective residual size from frontends. Removed field had
different semantics, which looks useless, and was never passed through
by any frontend.

While there, fix kern_data_resid field support in case of HA, missed in
r312291.