PCI: remove pci_assign_resource_fixed()

Adrian commented out this function in 2baad5f9

, but I don't think
it's even worth cluttering the file with the unused code.

Signed-off-by: Bjorn Helgaas <bjorn.helgaas@hp.com>
Signed-off-by: Jesse Barnes <jbarnes@virtuousgeek.org>