hostdev: Remove virHostdevGetActivePCIHostDeviceList()

hostdev: Remove virHostdevGetActivePCIHostDeviceList()

virHostdevGetPCIHostDeviceList() is similar but does not filter out
devices that are not in the active list; that said, we are looking
up the device in the active list just a few lines after anyway, so
we might as well just keep a single function around.

This also helps stress the fact the objects contained in pcidevs are
only for looking up the actual devices, which is something later
commits will make even more explicit.