Remove stale Debian packaging data (#8513)

## Summary of Changes

- The Debian packaging for unstable is tracked at
https://salsa.debian.org/reichel/cgal.
- No real need to track the Debian packaging for stable and testing in
VCS, the changes are usually minimal and can be recovered from the
published packages or the description in README.
- Remove stale tagging information from README.
- Remote stale uploading information from README.
- Update announcement text.

## Release Management

* Affected package(s): none
* License and copyright ownership: unchanged

Maintenance/deb/ANNOUNCEMENT.final

@@ -1,18 +1,19 @@
-Debian packages for CGAL 4.1 are now available as well. Simply add
+Debian packages for CGAL 6.0 are now available as well. Simply add
 
-  deb ftp://ftp.mpi-sb.mpg.de/pub/outgoing/CGAL/debian squeeze main
-  deb-src ftp://ftp.mpi-sb.mpg.de/pub/outgoing/CGAL/debian squeeze main
+  deb http://debian.cgal.org bullseye main
+  deb-src http://debian.cgal.org bullseye main
 
-  deb ftp://ftp.mpi-sb.mpg.de/pub/outgoing/CGAL/debian wheezy main
-  deb-src ftp://ftp.mpi-sb.mpg.de/pub/outgoing/CGAL/debian wheezy main
+  deb http://debian.cgal.org bookworm main
+  deb-src http://debian.cgal.org bookworm main
 
-to /etc/apt/sources list (you only need the pair of lines corresponding
-to the release you are using). For sid, packages should be available
-from the official Debian repository in a few days. The packages are called
-libcgal10, libcgal-dev, libcgal-qt4-10. libcgal-qt4-dev, libcgal-demo, and
-libcgal-ipelets.
+to /etc/apt/sources.list (you only need the pair of lines
+corresponding to the release you are using) and make sure that the
+package apt-transport-https is installed. For sid/unstable,
+packages are available from the official Debian repository. The
+packages are called libcgal-dev, libcgal-qt6-dev, libcgal-demo,
+and libcgal-ipelets.
 
 In case you want to download the packages manually, have a look at
-ftp://ftp.mpi-sb.mpg.de/pub/outgoing/CGAL/debian/pool/main/c/cgal/
+https://debian.cgal.org/pool/main/c/cgal/ .
 
 See also https://www.cgal.org/FAQ.html#debian_packages .

Maintenance/deb/README

@@ -4,54 +4,10 @@ README
 Backports
 ---------
 
-backport for wheezy:
+backport for trixie:
 - debian/changelog:
-  * adjust version suffix from -X to -X~wheezy1
-  * adjust suite from unstable to testing
+  * add new section with version suffix ...-X~deb13u1 and suite testing
 
-backport for squeeze:
+backport for bookworm:
 - debian/changelog:
-  * adjust version suffix from -X to -X~squeeze1
-  * adjust suite from unstable to stable
-- debian/control
-  * adjust Standards-Version from 3.9.3 to 3.9.1
-  * replace libgmp10-dev by libgmp3-dev (twice)
-  * adjust debhelper minimum version from 9 to 8
-- debian/compat
-  * adjust debhelper compatibility version from 9 to 8
-
-
-Tags
-----
-
-svn copy $SVNROOT/branches/next/Maintenance/deb/sid/debian $SVNROOT/tags/debian/4.1-1 -m "Tag for revision 4.1-1"
-svn copy $SVNROOT/branches/next/Maintenance/deb/wheezy/debian $SVNROOT/tags/debian/4.1-1~wheezy1 -m "Tag for revision 4.1-1~wheezy1"
-svn copy $SVNROOT/branches/next/Maintenance/deb/squeeze/debian $SVNROOT/tags/debian/4.1-1~squeeze1 -m "Tag for revision 4.1-1~squeeze1"
-
-
-FTP server
-----------
-
-# on my server
-cd /var/tmp
-tar xjf cgal.org-debian-repository.tar.bz2
-cd cgal.org-debian-repository
-mv pool/main/c/cgal/* archive
-reprepro -b . include wheezy|squeeze /path/to/*.changes
-cd ..
-tar cjf cgal.org-debian-repository.tar.bz2 cgal.org-debian-repository
-cd cgal.org-debian-repository
-rm -fr archive conf db
-tar cjf /srv/www/www.joachim-reichel.de/tmp/cgal.tar.bz2 .
-cd ..
-rm -fr cgal.org-debian-repository
-
-# on MPI machine
-cd /tmp
-wget http://www.joachim-reichel.de/tmp/cgal.tar.bz2
-su cgal
-cd /ftp/pub/outgoing/CGAL/debian
-mv pool/main/c/cgal/* archive
-rm -fr dists pool
-tar xjf /tmp/cgal.tar.bz2
-# There should be 3 subdirectories "archive", "dists", and "pool" now.
+  * add new section with version suffix ...-X~deb12u1 and suite stable