The forward declaration for shmem_should_replace_page() and
shmem_replace_page() is unnecessary.  Remove them.

Link: https://lkml.kernel.org/r/20210812120350.49801-4-linmiaohe@huawei.comSigned-off-by: NMiaohe Lin <linmiaohe@huawei.com>
Cc: Hugh Dickins <hughd@google.com>
Signed-off-by: NAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: NLinus Torvalds <torvalds@linux-foundation.org>