Fix apropos bug, wansn't getting into sly-mode

* sly.el (sly-apropos-mode): Get into `sly-mode'.
[top-level]: require 'apropos
Abandon sly-mrepl--freeze temporarily until better idea.

* contrib/sly-mrepl.el (sly-mrepl--freeze, sly-mrepl--unfreeze):
Make noops, had problems, have to study a better idea.
Fix indentation of DESTRUCTURE-CASE

* lib/lisp/swank.lisp (destructure-case): Changing from &rest do
&body is enough to make DESTRUCTURE-CASE indent correctly with the
`sly-indentation' contrib active.