Merge bitcoin/bitcoin#34671: doc: Update Guix install for Debian/Ubuntu

faa70ca764 doc: Update Guix install for Debian/Ubuntu (MarcoFalke)

Pull request description:

  Fixes https://github.com/bitcoin/bitcoin/issues/33982

ACKs for top commit:
  achow101:
    ACK faa70ca764
  willcl-ark:
    ACK faa70ca764
  janb84:
    this was discussed enough ACK faa70ca764

Tree-SHA512: 7f60a3fcd21706cb374b362f03b6cf8144dae4caf85f4c8ce6b3ed0311f380ba4f8195dcf7225ac7b6ec09919c1d7c9c5f77db80546980426dfc267e1884f8d0

contrib/guix/INSTALL.md

@@ -69,13 +69,13 @@ distros, please see: https://repology.org/project/guix/versions
 
 ### Debian / Ubuntu
 
-Guix is available as a distribution package in various versions of [Debian
+Currently, the `guix` package is no longer present in recent Debian or Ubuntu
-](https://packages.debian.org/search?keywords=guix) and [Ubuntu
+repositories. Any other installation option mentioned in this document may be
-](https://packages.ubuntu.com/search?keywords=guix).
+used.
 
-To install:
+If you previously installed `guix` via `apt`, you can remove it with:
 ```sh
-sudo apt install guix
+sudo apt purge guix
 ```
 
 ### Arch Linux