mm: remove unused has_isolate_pageblock

mm: remove unused has_isolate_pageblock

has_isolate_pageblock() has been unused since commit 55612e80e722 ("mm:
page_alloc: close migratetype race between freeing and stealing")

Remove it.

Link: https://lkml.kernel.org/r/20241018092235.2764859-1-kaixa@kiloview.com
Signed-off-by: Luoxi Li <kaixa@kiloview.com>
Acked-by: David Hildenbrand <david@redhat.com>
Reviewed-by: Muhammad Usama Anjum <usama.anjum@collabora.com>
Acked-by: Johannes Weiner <hannes@cmpxchg.org>
Reviewed-by: Anshuman Khandual <anshuman.khandual@arm.com>
Cc: Baolin Wang <baolin.wang@linux.alibaba.com>
Cc: Vlastimil Babka <vbabka@suse.cz>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>