Remove various Heap* types.

Also removed a bunch of trace() methods which
I touched by accident.  Turns out they're
all very interconnected sadly.

I re-wrote Supplement to not use templates
in an earlier version of this patch
but hit some trouble with vtables
and decided to table that work
for a later time once more of oilpan
has been unwound.

R=abarth@chromium.org

Review URL: https://codereview.chromium.org/683703003