m68k/mac: fix baboon irq disable and shutdown

The baboon_disabled hack is broken because it is missing an irq shutdown method. So releasing a Baboon irq kills the other Baboon irqs. But we don't really need this hack because we don't have media bay support and TREX uses a NuBus IRQ. Remove it.

Signed-off-by: Finn Thain <fthain@telegraphics.com.au>
Signed-off-by: Geert Uytterhoeven <geert@linux-m68k.org>