PCI/MSI: Remove empty pci_msi_init_pci_dev()

4a7cc831 ("genirq/MSI: Move msi_list from struct pci_dev to struct
device") removed the contents of pci_msi_init_pci_dev().  All
implementation of it are now empty, so remove it completely.

Signed-off-by: Bjorn Helgaas <bhelgaas@google.com>