PCI/MSI: Kill default_teardown_msi_irqs()

It doesn't have any caller left.

Link: https://lore.kernel.org/r/20210330151145.997953-10-maz@kernel.org


Signed-off-by: Marc Zyngier <maz@kernel.org>
Signed-off-by: Lorenzo Pieralisi <lorenzo.pieralisi@arm.com>
Acked-by: Bjorn Helgaas <bhelgaas@google.com>