PCI: Remove function pcim_intx() prototype from pci.h

PCI: Remove function pcim_intx() prototype from pci.h

The subsystem-internal header pci.h still contains the function
prototype of pcim_intx(), which has since been made public in the global
header.

Remove the redundant function prototype.

Signed-off-by: Philipp Stanner <phasta@kernel.org>
[kwilczynski: commit log]
Signed-off-by: Krzysztof Wilczyński <kwilczynski@kernel.org>
Reviewed-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
Link: https://lore.kernel.org/r/20250522084626.150148-2-phasta@kernel.org