Actually leave one in contrib/sly-cl-indent.el that I have to analyse.

* sly.el: Replace functions from 'cl with their cl-lib
counterparts.
(require): Don't require 'cl, not even when compiling.
(sly-read-symbol-name): Move down to avoid compiler warning.
(sly-def-connection-var): Use gv-define-setter, not defsetf.
(sly--this-inspector-name): Move up to avoid compiler warning.

* contrib/sly-mrepl.el: Replace functions from 'cl with their cl-lib
counterparts.

* contrib/sly-stickers.el: Replace functions from 'cl with their cl-lib
counterparts.