refactor(cli): remove :stub, :obsolete, :deprecated, :since

I've removed these CLI properties because they were either
unused (:deprecated and :since) or poorly implemented (:stub and
:obsolete). And I'd rather have fewer magical properties, and instead
delegate these roles to the defobsolete! and (new) defstub!  macros.
Also, in the future, the help API will ascertain :since dynamically, so
it won't be very useful.

In summary:
- Use defstub! instead of :stub
- Use defobsolete! instead of :obsolete or :deprecated
- This removes the doom-cli-deprecated-error type (it's not really an
  error to begin with).
- Removes :stub, :obsolete, :deprecated, and :since

core/cli/make/completions.el

@@ -18,7 +18,6 @@
      ;; TODO (outfile ("-o" "--outfile" file))
      &context context &args args)
   "Generate completion scripts for a Doom-CLI script."
-  ;; :stub t
   ;; (unless outfile
   ;;   (user-error "No destination file specified"))
   (let ((shell (or shell (file-name-base (getenv "SHELL"))))