Cleanup destruction of heap objects

Generate the code from a macro instead of duplicating boiler
plate code. Operate on Heap::Base instead of Managed.

Change-Id: I84c5a705980899be3e5b931a093645e50d3923bf
Reviewed-by: Simon Hausmann <simon.hausmann@digia.com>
Let the memory manager operate on Heap::Base objects, not Managed

Change-Id: Ib5c9b51dbf9c69abeda088094e6348dd545bf3c8
Reviewed-by: Simon Hausmann <simon.hausmann@digia.com>