zpool: remove the list of pools_head

The list of pools_head is no longer needed because the caller has been
deleted in commit 479305fd ("zpool: remove zpool_evict()").

Link: https://lkml.kernel.org/r/20211215163727.GA17196@pcSigned-off-by: Zhaoyu Liu <zackary.liu.pro@gmail.com>
Cc: Dan Streetman <ddstreet@ieee.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

mm/zpool.c

@@ -24,16 +24,11 @@ struct zpool {
 	const struct zpool_ops *ops;
 	bool evictable;
 	bool can_sleep_mapped;
-
-	struct list_head list;
 };
 
 static LIST_HEAD(drivers_head);
 static DEFINE_SPINLOCK(drivers_lock);
 
-static LIST_HEAD(pools_head);
-static DEFINE_SPINLOCK(pools_lock);
-
 /**
  * zpool_register_driver() - register a zpool implementation.
  * @driver:	driver to register
@@ -195,10 +190,6 @@ struct zpool *zpool_create_pool(const char *type, const char *name, gfp_t gfp,
 
 	pr_debug("created pool type %s\n", type);
 
-	spin_lock(&pools_lock);
-	list_add(&zpool->list, &pools_head);
-	spin_unlock(&pools_lock);
-
 	return zpool;
 }
 
@@ -217,9 +208,6 @@ void zpool_destroy_pool(struct zpool *zpool)
 {
 	pr_debug("destroying pool type %s\n", zpool->driver->type);
 
-	spin_lock(&pools_lock);
-	list_del(&zpool->list);
-	spin_unlock(&pools_lock);
 	zpool->driver->destroy(zpool->pool);
 	zpool_put_driver(zpool->driver);
 	kfree(zpool);