PCI: Remove unused SR-IOV VF Migration support

This reverts commit 74bb1bcc7dbb ("PCI: handle SR-IOV Virtual Function
Migration"), removing this exported interface:

  pci_sriov_migration()

Since pci_sriov_migration() is unused, it is impossible to schedule
sriov_migration_task() or use any of the other migration infrastructure.

This is based on Stephen Hemminger's patch (see link below), but goes a bit
further.

Link: http://lkml.kernel.org/r/20131227132710.7190647c@nehalam.linuxnetplumber.net
Signed-off-by: Bjorn Helgaas <bhelgaas@google.com>
CC: Stephen Hemminger <stephen@networkplumber.org>