mm: remove unused pgdat->inactive_ratio

mm: remove unused pgdat->inactive_ratio

Since commit 59dc76b0d4df ("mm: vmscan: reduce size of inactive file
list") 'pgdat->inactive_ratio' is not used, except for printing
"node_inactive_ratio: 0" in /proc/zoneinfo output.

Remove it.

Link: http://lkml.kernel.org/r/20171003152611.27483-1-aryabinin@virtuozzo.com
Signed-off-by: Andrey Ryabinin <aryabinin@virtuozzo.com>
Reviewed-by: Rik van Riel <riel@redhat.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>