PCI: Removed unused parts of Page Request Interface support

My philosophy is unused code is dead code.  And dead code is subject to bit
rot and is a likely source of bugs.  Use it or lose it.

This reverts parts of c320b976d783 ("PCI: Add implementation for PRI
capability"), removing these interfaces:

    pci_pri_enabled()
    pci_pri_stopped()
    pci_pri_status()

[bhelgaas: split to separate patch]
Signed-off-by: Stephen Hemminger <stephen@networkplumber.org>
Signed-off-by: Bjorn Helgaas <bhelgaas@google.com>
CC: Joerg Roedel <joro@8bytes.org>