iommu/amd: Remove unused variable

Remove 'amd_iommu_aperture_order' as its not used since commit d9cfed9.

Signed-off-by: Vasant Hegde <vasant.hegde@amd.com>
Reviewed-by: Jason Gunthorpe <jgg@nvidia.com>
Link: https://lore.kernel.org/r/20250227162320.5805-3-vasant.hegde@amd.com
Signed-off-by: Joerg Roedel <jroedel@suse.de>

drivers/iommu/amd/amd_iommu_types.h

@@ -928,9 +928,6 @@ struct unity_map_entry {
  * Data structures for device handling
  */
 
-/* size of the dma_ops aperture as power of 2 */
-extern unsigned amd_iommu_aperture_order;
-
 extern bool amd_iommu_force_isolation;
 
 /* Max levels of glxval supported */