bug#53885: Autoload package-installed-p

[Corwin Brust]

retitle 53885 28.0.91 [PATCH] Autoload package-installed-p
thanks

I inadvertently included an explicit call to `require' in the
reproducer, which functions as a work-around for this (IMO) missing
autoload. Sorry for any confusion caused.

>
> Reproducer:
>
> NOTE: Make sure you have a folder beneth your home directory called
> "elpa" and that it is empty.
>
> Launch emacs -Q
> Insert and evaluate:

Corrected reproducer:

(progn
  (setq package-user-dir "~/elpa")
  (setq package-archives
    '(("MELPA" .
    "https://melpa.org/packages/";)))
  (unless (package-installed-p 'use-package)
    (package-install 'use-package)))