remove _resolve_label and related attributes

remove _resolve_label and related attributes

these seem to date back to 0.9 and revs like #3148 but none
of it seems to be affecting things now, try removing it all
and seeing what fails.

we've noted that _resolve_label does not appear to be
needed, however allow_label_resolve remains relevant both
for non-column elements like text() as well as that it is
used explicitly by the joined eager loader.

Change-Id: Ic8a5d8001ef2a4133360f51a92a6f7b0cc389095