Function-quote completion property of declare form

Function-quote completion property of declare form

For discussion, see the following thread:
https://lists.gnu.org/r/emacs-devel/2021-02/msg01666.html

* lisp/emacs-lisp/byte-run.el (byte-run--set-completion): Quote with
'function' for syntactical consistency with other declare form
properties.  This allows writing (declare (completion foo)) instead
of (declare (completion 'foo)).
* lisp/emacs-lisp/easymenu.el (easy-menu-do-define):
* lisp/gnus/gnus-sum.el (gnus-summary-make-menu-bar): Prefer
function-put over put for function symbols.
* lisp/subr.el (ignore, undefined): Remove #'-quoting from declare
form; it is no longer needed.