PCI/PM: Remove unused PCI_PM_BUS_WAIT

476e7fae ("PCI PM: Do not wait for buses in B2 or B3 during resume")
removed the last use of PCI_PM_BUS_WAIT.  Remove the definition as well.

Signed-off-by: Bjorn Helgaas <bhelgaas@google.com>
Reviewed-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>