hw/mips/mips_jazz: Remove no-longer-necessary override of do_unassigned_access

Now that the MIPS CPU implementation uses the new
do_transaction_failed hook, we can remove the old code that handled
the do_unassigned_access hook.

Signed-off-by: Peter Maydell <peter.maydell@linaro.org>
Signed-off-by: Aleksandar Markovic <amarkovic@wavecomp.com>
Reviewed-by: Philippe Mathieu-Daudé <philmd@redhat.com>
Tested-by: Hervé Poussineau <hpoussin@reactos.org>
Message-Id: <20190802160458.25681-4-peter.maydell@linaro.org>