Revert "PCI/MSI: Provide stubs for IMS functions"

This reverts commit 41efa431.

IMS (Interrupt Message Store) support appeared in v6.2, but there are no
users yet.

Remove it for now.  We can add it back when a user comes along.  If this is
re-added later, this could be squashed with these commits:

  0194425a ("PCI/MSI: Provide IMS (Interrupt Message Store) support")
  c9e5bea2 ("PCI/MSI: Provide pci_ims_alloc/free_irq()")

which added the non-stub implementations.

Link: https://lore.kernel.org/r/20240410221307.2162676-2-helgaas@kernel.org


Signed-off-by: Bjorn Helgaas <bhelgaas@google.com>
Reviewed-by: Kevin Tian <kevin.tian@intel.com>
Reviewed-by: Thomas Gleixner <tglx@linutronix.de>