PCI: Remove pcim_iounmap_regions()

All users of the deprecated function pcim_iounmap_regions() have been
ported by now. Remove it.

Signed-off-by: Philipp Stanner <pstanner@redhat.com>
Signed-off-by: Bjorn Helgaas <bhelgaas@google.com>
Reviewed-by: Zijun Hu <quic_zijuhu@quicinc.com>
Reviewed-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
Link: https://patch.msgid.link/20250327110707.20025-4-phasta@kernel.org