Revert "genirq: Add fasteoi IPI flow"

handle_percpu_devid_fasteoi_ipi() has no more users, and
handle_percpu_devid_irq() can do all that it was supposed to do. Get rid of
it.

This reverts commit c5e5ec03

.

Signed-off-by: Valentin Schneider <valentin.schneider@arm.com>
Signed-off-by: Marc Zyngier <maz@kernel.org>
Link: https://lore.kernel.org/r/20201109094121.29975-6-valentin.schneider@arm.com