PCI/MSI: Remove unused pci_msi_create_default_irq_domain()

pci_msi_create_default_irq_domain() is never called in the whole tree, so
remove it as well as all the supporting code for a default PCI MSI domain.

Signed-off-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Bjorn Helgaas <bhelgaas@google.com>
Reviewed-by: Thomas Gleixner <tglx@linutronix.de>