mm: remove lru_add_drain_all in alloc_contig_range

__alloc_contig_migrate_range already has lru_add_drain_all call via
migrate_prep.  It's necessary to move LRU taget pages into LRU list to be
able to isolated.  However, lru_add_drain_all call after
__alloc_contig_migrate_range is pointless since it has changed source page
freeing from putback_lru_pages to put_page[1].

This patch removes it.

[1] c6c919eb

, ("mm: use put_page() to free page instead of putback_lru_page()"

Link: https://lkml.kernel.org/r/20210303204512.2863087-1-minchan@kernel.org
Signed-off-by: Minchan Kim <minchan@kernel.org>
Reviewed-by: Oscar Salvador <osalvador@suse.de>
Acked-by: Vlastimil Babka <vbabka@suse.cz>
Acked-by: Michal Hocko <mhocko@suse.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>