PCI/MSI: Remove unused __write_msi_msg() and write_msi_msg()

Remove unused __write_msi_msg() and write_msi_msg().

These were added by 83a18912 ("PCI/MSI: Rename write_msi_msg() to
pci_write_msi_msg()"), they served their purpose, and they're no longer
needed.

Signed-off-by: Bjorn Helgaas <bhelgaas@google.com>
CC: Jiang Liu <jiang.liu@linux.intel.com>	# 83a18912 author