ACPI: Remove acpi_pci_bind_root() definition

Noticed that acpi_pci_bind_root(), which has been deleted,
is left defined in acpi_driver.h.  So delete this definition
from the header as well.

Signed-off-by: Toshi Kani <toshi.kani@hp.com>
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>