Drop obsolete Debian&Ubuntu-related info that is no longer relevant.

Author: sten0

README.md

@@ -48,8 +48,6 @@ PHP Mode is available from [package systems provided by several OSs][php-mode-pa
 
 Please consider installing the package provided in `sid` (aka: "unstable", a rolling release) in order to benefit from the latest PHP Mode features and performance improvements.  The latest version can be found here: [`elpa-php-mode`][elpa-php-mode].  Investigate "apt-pinning" to make tracking this update stream automatic.
 
-Also, the `php-elisp` package provided by [Debian 9 (stretch)][php-elisp-stretch] and [Ubuntu 18.10][php-elisp-ubuntu1810] and earlier is [extremely old][issue-430], so **PLEASE DO NOT INSTALL IT**.
-
 ### Manual installation
 
 If you don't want to depend on a package manager, you can install Lisp files directly in the traditional way.  See [Manual installation][wiki-manual-installation] for our recommended setup method.
@@ -332,7 +330,6 @@ This project was maintained by [Eric James Michael Ritz][@ejmr] until 2017. Curr
 [cc mode]: https://www.gnu.org/software/emacs/manual/html_mono/ccmode.html
 [elpa-php-mode]: https://packages.debian.org/sid/elpa-php-mode
 [gpl-v3]: https://www.gnu.org/licenses/quick-guide-gplv3.html
-[issue-430]: https://github.com/emacs-php/php-mode/issues/430
 [nongnu-devel-elpa-badge]: https://elpa.nongnu.org/nongnu-devel/php-mode.svg
 [nongnu-devel-elpa]: https://elpa.nongnu.org/nongnu-devel/php-mode.html
 [nongnu-elpa-badge]: https://elpa.nongnu.org/nongnu/php-mode.svg
@@ -342,8 +339,6 @@ This project was maintained by [Eric James Michael Ritz][@ejmr] until 2017. Curr
 [melpa-stable-badge]: http://stable.melpa.org/packages/php-mode-badge.svg
 [melpa-stable-link]: http://stable.melpa.org/#/php-mode
 [package]: https://www.gnu.org/software/emacs/manual/html_node/emacs/Packages.html
-[php-elisp-stretch]: https://packages.debian.org/stretch/php-elisp
-[php-elisp-ubuntu1810]: https://packages.ubuntu.com/cosmic/php-elisp
 [php-mode-packages]: https://repology.org/project/emacs:php-mode/versions
 [php-mode]: https://github.com/emacs-php/php-mode
 [php-suite]: https://github.com/emacs-php/php-suite