zsmalloc: remove synchronize_rcu from zs_compact()

Do not synchronize rcu in zs_compact(). Neither zsmalloc not
zram use rcu.

Signed-off-by: Sergey Senozhatsky <sergey.senozhatsky@gmail.com>
Acked-by: Minchan Kim <minchan@kernel.org>
Cc: Nitin Gupta <ngupta@vflare.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

mm/zsmalloc.c

@@ -1778,8 +1778,6 @@ unsigned long zs_compact(struct zs_pool *pool)
 		nr_migrated += __zs_compact(pool, class);
 	}
 
-	synchronize_rcu();
-
 	return nr_migrated;
 }
 EXPORT_SYMBOL_GPL(zs_compact);