Removed some dead-code, and some dump logic in deferred field loading
and deferred model reduce(). The biggest user visible change is
that primary keys do not need fetching from the DB in some inheritance
All tests pass on SQLite.
[1/2] #18343 -- Cleaned up deferred model implementation
Generic cleanup and dead code removal in deferred model field loading
I splitted the patches into two for easier review.
[2/2] #18343 -- deferred model pk handling in inheritance case
Assuming an inherited model with parent_ptr_id -> id, doing a deferred
load and then fetching the id field would cause a database query, even
if the id field's value is already loaded in the parent_ptr_id field.
Pushed in manually