PCI: Remove unused 'node' member from struct pci_driver

Remove the unused 'node' member. It got replaced by device_driver chaining
more than 20 years ago in commit 4b4a837f2b57 ("PCI: start to use common
fields of struct device_driver more...") of the history.git tree.

Link: https://lore.kernel.org/r/20231220133505.8798-1-minipli@grsecurity.net
Signed-off-by: Mathias Krause <minipli@grsecurity.net>
Signed-off-by: Bjorn Helgaas <bhelgaas@google.com>
Acked-by: Kalle Valo <kvalo@kernel.org>