Remove an incorrect ColumnMap callback which fires every time

We no longer need to be backwards compatible with 3.6 (as 3.8 needed to
be, hence e8fa18d).  Keep the non-standard callback name, however, as
renaming would ensure *all* callbacks for this ColumnMap broke.
Provide record-specific column maps with access to the generic column map

This lets specific maps (and their callbacks) re-use parts of the
generic map when locally overriding them for a record type.
Merge branch '4.2/access-to-generic-column-map'