mm: remove folio_test_anon(folio)==false path in __folio_add_anon_rmap()

mm: remove folio_test_anon(folio)==false path in __folio_add_anon_rmap()

The folio_test_anon(folio)==false cases has been relocated to
folio_add_new_anon_rmap().  Additionally, four other callers consistently
pass anonymous folios.

stack 1:
remove_migration_pmd
   -> folio_add_anon_rmap_pmd
     -> __folio_add_anon_rmap

stack 2:
__split_huge_pmd_locked
   -> folio_add_anon_rmap_ptes
      -> __folio_add_anon_rmap

stack 3:
remove_migration_pmd
   -> folio_add_anon_rmap_pmd
      -> __folio_add_anon_rmap (RMAP_LEVEL_PMD)

stack 4:
try_to_merge_one_page
   -> replace_page
     -> folio_add_anon_rmap_pte
       -> __folio_add_anon_rmap

__folio_add_anon_rmap() only needs to handle the cases
folio_test_anon(folio)==true now.
We can remove the !folio_test_anon(folio)) path within
__folio_add_anon_rmap() now.

Link: https://lkml.kernel.org/r/20240617231137.80726-4-21cnbao@gmail.com
Signed-off-by: Barry Song <v-songbaohua@oppo.com>
Suggested-by: David Hildenbrand <david@redhat.com>
Tested-by: Shuai Yuan <yuanshuai@oppo.com>
Acked-by: David Hildenbrand <david@redhat.com>
Cc: Baolin Wang <baolin.wang@linux.alibaba.com>
Cc: Chris Li <chrisl@kernel.org>
Cc: "Huang, Ying" <ying.huang@intel.com>
Cc: Matthew Wilcox (Oracle) <willy@infradead.org>
Cc: Michal Hocko <mhocko@suse.com>
Cc: Ryan Roberts <ryan.roberts@arm.com>
Cc: Suren Baghdasaryan <surenb@google.com>
Cc: Yang Shi <shy828301@gmail.com>
Cc: Yosry Ahmed <yosryahmed@google.com>
Cc: Yu Zhao <yuzhao@google.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>