iommu: remove stale declaration left over by a merge conflict

The merge commit ae3325f ("Merge branches 'arm/smmu', 'mediatek',
's390', 'ti/omap', 'riscv' and 'core' into next") left a stale
declaration of 'iommu_present()' even though the 'core' branch that was
merged had removed the function (and the declaration).

Remove it for real.

Reported-by: Dmitry Safonov <0x7f454c46@gmail.com>
Cc: Joerg Roedel <jroedel@suse.de>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

include/linux/iommu.h

@@ -841,7 +841,6 @@ static inline void iommu_iotlb_gather_init(struct iommu_iotlb_gather *gather)
 	};
 }
 
-extern bool iommu_present(const struct bus_type *bus);
 extern bool device_iommu_capable(struct device *dev, enum iommu_cap cap);
 extern bool iommu_group_has_isolated_msi(struct iommu_group *group);
 struct iommu_domain *iommu_paging_domain_alloc_flags(struct device *dev, unsigned int flags);