lib/stackdepot: fix comment in include/linux/stackdepot.h

As stack traces can now be evicted from the stack depot, remove the
comment saying that they are never removed.

Link: https://lkml.kernel.org/r/0e[e-mail]
Fixes: 108be8def46e ("lib/stackdepot: allow users to evict stack traces")
Signed-off-by: Andrey Konovalov <[e-mail]>
Reviewed-by: Marco Elver <[e-mail]>
Cc: Alexander Potapenko <[e-mail]>
Cc: Dmitry Vyukov <[e-mail]>
Cc: Evgenii Stepanov <[e-mail]>
Cc: Tetsuo Handa <[e-mail]>
Cc: Vlastimil Babka <[e-mail]>
Signed-off-by: Andrew Morton <[e-mail]>

include/linux/stackdepot.h

···
  * SLUB_DEBUG needs 256 bytes per object for that). Since allocation and free
  * stack traces often repeat, using stack depot allows to save about 100x space.
  *
- * Stack traces are never removed from the stack depot.
- *
  * Author: Alexander Potapenko <[e-mail]>
  * Copyright (C) 2016 Google, Inc.
  *