Complete removal of `contrib/sly-c-p-c` and fix tests

* contrib/sly-fuzzy.el (sly-fuzzy-abort): Check for target buffer
liveness.

* contrib/sly-package-fu.el (require): Don't require `sly-c-p-c'

* contrib/test/sly-fuzzy-tests.el (sly-fuzzy): New file with some
basic tests for sly-fuzzy.

* doc/slime.texi (Compound Completion): Remove section.

* doc/slime.texi (Shortcuts): Remove section.
(Emacs-side customization): Don't mention `sly-complete-symbol*'
Fix more tests

* contrib/test/sly-mrepl-tests.el
(sly-mrepl-tests--assert-dedicated-stream): New helper function.
(basic-repl-setup): Call it.

* contrib/test/sly-parse-tests.el (sly-check-buffer-form):
Removed.
(form-up-to-point.1): Fix tests. Use `should.