[MSC2-32] Removing dependencies support between tasks.
[MSC2-32] Simplyfing TaskControllerImpl state machine after dependencies support removal.
[MSC2-32] Removing useless FLAG_USER_THREAD from TaskControllerImpl  because tasks are not visible to MSC2 API users.
[MSC2-32] Removing useless FLAG_EXECUTE_DONE flag from TaskControllerImpl.
[MSC2-32] Eliminating useless TaskBuilder.release() return value.
[MSC2-20] Eliminating good-for-nothing transaction fields - no functional change.
[MSC2-20] Eliminating useless TaskBuilder methods.
WIP
WIP
WIP - fixing broken txn restart
WIP
WIP