PCI: Remove unused pci_pool wrappers

The pci_pool users have been converted to dma_pool.  Remove the unused
pci_pool wrappers.

Link: https://lore.kernel.org/r/20211018124110.214-1-caihuoqing@baidu.com


Signed-off-by: Cai Huoqing <caihuoqing@baidu.com>
Signed-off-by: Bjorn Helgaas <bhelgaas@google.com>