[S390] Remove unncessary export of arch_pick_mmap_layout

This function is defined for use in exec, not in modules.
No other architecture exports its implementation.
Signed-off-by: Ben Hutchings <ben@decadent.org.uk>
Signed-off-by: Martin Schwidefsky <schwidefsky@de.ibm.com>

arch/s390/mm/mmap.c

@@ -100,7 +100,6 @@ void arch_pick_mmap_layout(struct mm_struct *mm)
 		mm->unmap_area = arch_unmap_area_topdown;
 	}
 }
-EXPORT_SYMBOL_GPL(arch_pick_mmap_layout);
 
 #else
 
@@ -175,6 +174,5 @@ void arch_pick_mmap_layout(struct mm_struct *mm)
 		mm->unmap_area = arch_unmap_area_topdown;
 	}
 }
-EXPORT_SYMBOL_GPL(arch_pick_mmap_layout);
 
 #endif