iommu: Remove iommu_group_get_by_id()

This is never called.

Signed-off-by: Jason Gunthorpe <jgg@nvidia.com>
Reviewed-by: Robin Murphy <robin.murphy@arm.com>
Link: https://lore.kernel.org/r/0-v1-60bbc66d7e92+24-rm_iommu_get_by_id_jgg@nvidia.com


Signed-off-by: Joerg Roedel <jroedel@suse.de>