cl deprecation warning on emacs 27

[stuart-little]

Every time I start emacs 27.2.50 with

(if (file-exists-p "~/quicklisp/slime-helper.el")
  (load (expand-file-name "~/quicklisp/slime-helper.el")))

at the top of my init file I get a warning:

Package cl is deprecated

This doesn't happen if I comment out those lines from my init file. I figure this happens because the quicklisp slime package is still requiring 'cl:

$ ack "require 'cl[^-]" ~/quicklisp/ | ack '2\.26'
---
$HOME/quicklisp/dists/quicklisp/software/slime-v2.26.1/slime.el:66:(eval-when-compile (require 'cl)) ; defsetf, lexical-let
$HOME/quicklisp/dists/quicklisp/software/slime-v2.26.1/contrib/slime-presentations.el:5:  (require 'cl))
$HOME/quicklisp/dists/quicklisp/software/slime-v2.26.1/contrib/slime-sprof.el:3:(eval-when-compile (require 'cl)) ; lexical-let*
$HOME/quicklisp/dists/quicklisp/software/slime-v2.26.1/contrib/slime-tramp.el:3:(eval-when-compile (require 'cl)) ; lexical-let
$HOME/quicklisp/dists/quicklisp/software/slime-v2.26.1/contrib/slime-repl.el:20:(eval-when-compile (require 'cl)) ; slime-def-connection-var, which
$HOME/quicklisp/dists/quicklisp/software/slime-v2.26.1/contrib/slime-cl-indent.el:46:(eval-when-compile (require 'cl))
$HOME/quicklisp/dists/quicklisp/software/slime-v2.26.1/contrib/bridge.el:69:  (require 'cl))
$HOME/quicklisp/dists/quicklisp/software/slime-v2.26.1/contrib/slime-hyperdoc.el:4:(eval-when-compile (require 'cl)) ; lexical-let
$HOME/quicklisp/dists/quicklisp/software/slime-v2.26.1/contrib/slime-clipboard.el:5:  (require 'cl)) ; lexical-let
$HOME/quicklisp/dists/quicklisp/software/slime-v2.26.1/slime-tests.el:34:  (require 'cl)) ; lexical-let
$HOME/quicklisp/dists/quicklisp/software/slime-v2.26.1/slime-tests.el:1308:         `((require 'cl)
$HOME/quicklisp/dists/quicklisp/software/slime-v2.26.1/lib/cl-lib.el:73:(require 'cl)
$HOME/quicklisp/dists/quicklisp/software/slime-v2.26.1/lib/ert-x.el:58:  (require 'cl))
$HOME/quicklisp/dists/quicklisp/software/slime-v2.26.1/lib/ert.el:58:  (require 'cl))

On the other hand, the slime folks seem to have switched to (require 'cl-lib): if I clone that repo and do the same search in it, I get almost nothing:

<in cloned slime repo>$ ack "require 'cl[^-]" .
---
lib/cl-lib.el
73:(require 'cl)

lib/ert-x.el
58:  (require 'cl))

lib/ert.el
58:  (require 'cl))

This is despite the fact that they report the same 2.26.1 as the latest version. I am not even sure if this is an issue to report here or over in the slime org: the problem seems to be that the quicklisp version of slime is not quite up to date..