PCI: Remove unused pcibios_select_root() (again)

a6c140969b46 ("Delete pcibios_select_root") removed pcibios_select_root().
But a7db50405216 ("PCI: remove pcibios_scan_all_fns()") added a few copies
back, probably with some incorrect merge conflict resolutions.

Remove the still-unused pcibios_select_root() definitions.

Signed-off-by: Bjorn Helgaas <bhelgaas@google.com>