mm: remove obsolete comment above struct per_cpu_pages

Since commit 01b4445 ("mm/page_alloc: replace local_lock with normal
spinlock"), per_cpu_pages is protected by normal spinlock.  Remove the
obsolete comment as it's not that helpful.

Link: https://lkml.kernel.org/r/[email protected]
Signed-off-by: Miaohe Lin <[email protected]>
Signed-off-by: Andrew Morton <[email protected]>

Author: MiaoheLin

include/linux/mmzone.h

@@ -676,7 +676,6 @@ enum zone_watermarks {
 #define high_wmark_pages(z) (z->_watermark[WMARK_HIGH] + z->watermark_boost)
 #define wmark_pages(z, i) (z->_watermark[i] + z->watermark_boost)
 
-/* Fields and list protected by pagesets local_lock in page_alloc.c */
 struct per_cpu_pages {
 	spinlock_t lock;	/* Protects lists field */
 	int count;		/* number of pages in the list */