memory: remove memory_region_destroy

The function is empty after the previous patch, so remove it.

Reviewed-by: Peter Crosthwaite <peter.crosthwaite@xilinx.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>

include/exec/memory.h

@@ -429,15 +429,6 @@ void memory_region_init_iommu(MemoryRegion *mr,
                               const char *name,
                               uint64_t size);
 
-/**
- * memory_region_destroy: Destroy a memory region and reclaim all resources.
- *
- * @mr: the region to be destroyed.  May not currently be a subregion
- *      (see memory_region_add_subregion()) or referenced in an alias
- *      (see memory_region_init_alias()).
- */
-void memory_region_destroy(MemoryRegion *mr);
-
 /**
  * memory_region_owner: get a memory region's owner.
  *