Several doc fixes in package.el

Several doc fixes in package.el

* lisp/emacs-lisp/package.el (top-level)
(package-check-signature, package--from-builtin)
(package-desc-full-name, package-desc-suffix)
(package-desc--keywords, package--bi-desc)
(package-process-define-package, package-archive-base)
(package-install-from-archive, package-install-from-buffer)
(package-install-file, package-autoremove, describe-package-1)
(package-install-button-action, package-delete-button-action)
(package-keyword-button-action, package-make-button)
(package--print-email-button, package-list-unversioned)
(package--emacs-version-list, package-menu-toggle-hiding)
(package-hidden-regexps, package-menu-hide-package)
(package-menu-get-status, package-menu--find-upgrades)
(package-menu--post-refresh): Doc fixes.  (Bug#37410)