docs/vm: remove unused 3 items explanation for /proc/vmstat

Commit 5647bc293a ("mm: compaction: Move migration fail/success
stats to migrate.c"), removed 3 items in /proc/vmstat. but the docs
still has their explanation. let's remove them.

"compact_blocks_moved",
"compact_pages_moved",
"compact_pagemigrate_failed",

Link: https://lkml.kernel.org/r/1605520282-51993-1-git-send-email-alex.shi@linux.alibaba.com
Signed-off-by: Alex Shi <alex.shi@linux.alibaba.com>
Reviewed-by: Zi Yan <ziy@nvidia.com>
Cc: Jonathan Corbet <corbet@lwn.net>
Cc: Yang Shi <yang.shi@linux.alibaba.com>
Cc: "Kirill A. Shutemov" <kirill.shutemov@linux.intel.com>
Cc: David Rientjes <rientjes@google.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

Documentation/admin-guide/mm/transhuge.rst

@@ -401,21 +401,6 @@ compact_fail
 	is incremented if the system tries to compact memory
 	but failed.
 
-compact_pages_moved
-	is incremented each time a page is moved. If
-	this value is increasing rapidly, it implies that the system
-	is copying a lot of data to satisfy the huge page allocation.
-	It is possible that the cost of copying exceeds any savings
-	from reduced TLB misses.
-
-compact_pagemigrate_failed
-	is incremented when the underlying mechanism
-	for moving a page failed.
-
-compact_blocks_moved
-	is incremented each time memory compaction examines
-	a huge page aligned range of pages.
-
 It is possible to establish how long the stalls were using the function
 tracer to record how long was spent in __alloc_pages_nodemask and
 using the mm_page_alloc tracepoint to identify which allocations were