PCI: remove pci_find_slot from PCI_LEGACY config description

Commit 3b073eda

 has removed pci_find_slot, so there's no point in
mentioning it in the config description as one of the deprecated APIs
there are enabled by PCI_LEGACY and still used by some drivers.

Signed-off-by: Thadeu Lima de Souza Cascardo <cascardo@holoscopio.com>
Signed-off-by: Jesse Barnes <jbarnes@virtuousgeek.org>