rmap: remove anon_vma_link() nommu stub

anon_vma_link() is unused since commit 5beb493 ("mm: change anon_vma
linking to fix multi-process server scalability issue").

Link: https://lkml.kernel.org/r/cdce9b00c9ab15f6d02eddf40dcad537d3e9676f.1692877089.git.baruch@tkos.co.il
Signed-off-by: Baruch Siach <baruch@tkos.co.il>
Reviewed-by: David Hildenbrand <david@redhat.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

Author: baruchsiach

include/linux/rmap.h

@@ -479,7 +479,6 @@ struct anon_vma *folio_lock_anon_vma_read(struct folio *folio,
 
 #define anon_vma_init()		do {} while (0)
 #define anon_vma_prepare(vma)	(0)
-#define anon_vma_link(vma)	do {} while (0)
 
 static inline int folio_referenced(struct folio *folio, int is_locked,
 				  struct mem_cgroup *memcg,