PCI: Remove unused pci_fixup_irqs() function

Now we have removed all callers of pci_fixup_irqs() and migrated everything
to pci_assign_irq(), delete the pci_fixup_irqs() function completely.

Signed-off-by: Matthew Minter <matt@masarand.com>
[lorenzo.pieralisi@arm.com: updated commit log]
Signed-off-by: Lorenzo Pieralisi <lorenzo.pieralisi@arm.com>
Signed-off-by: Bjorn Helgaas <bhelgaas@google.com>