The function is unused after commit 1b932ced ("iommu:
Remove detach_dev callbacks") and so compilation fails with

drivers/iommu/ipmmu-vmsa.c:305:13: error: ‘ipmmu_utlb_disable’ defined but not used [-Werror=unused-function]
  305 | static void ipmmu_utlb_disable(struct ipmmu_vmsa_domain *domain,
      |             ^~~~~~~~~~~~~~~~~~

Remove the function to fix the compile error.

Fixes: 1b932ced ("iommu: Remove detach_dev callbacks")
Signed-off-by: Joerg Roedel <jroedel@suse.de>
Reviewed-by: Jason Gunthorpe <jgg@nvidia.com>
Link: https://lore.kernel.org/r/20230113185640.8050-1-joro@8bytes.org