packages: remove duplicate upgrade test debian

What

This MR removes the upgrade testing infrastructure for Debian/Ubuntu packages, specifically:

1. Removes the upgrade test script (docs/introduction/upgrade-bin-deb.sh) - a 116-line shell script that tested package upgrades from the current released version to the development version
2. Removes CI jobs that executed upgrade tests:
   • oc.upgrade_bin_debian_bookworm (Debian Bookworm)
   • oc.upgrade_bin_ubuntu_jammy (Ubuntu Jammy)
3. Cleans up CI pipeline configurations by removing references to the upgrade script from pipeline trigger conditions
4. Removes the job_upgrade_bin function from ci/bin/debian_repository.ml that generated these CI jobs

Why

The upgrade tests were designed to validate that users could successfully upgrade from the current released version of Octez packages to the development version being built in the CI. However, these tests appear to be:

• Duplicate functionality: The primary installation testing is already covered by the systemd upgrade tests
• Maintenance overhead: The upgrade script required maintaining parallel logic for repository configuration and package installation
• Unused in documentation: Unlike install-bin-deb.sh which is referenced in user documentation (docs/introduction/howtoget.rst and docs/introduction/serokell.rst), the upgrade script was only used internally by CI

Manually testing the MR

Reviewers should verify:

1. CI pipelines run successfully without the removed upgrade jobs
2. Installation tests still work - the oc.install_bin_* jobs should continue to function normally
3. No broken references - ensure no other scripts or documentation reference the removed upgrade script
4. Package installation documentation in docs/introduction/howtoget.rst and docs/introduction/serokell.rst remains accurate (these use install-bin-deb.sh, not the removed upgrade script)

The removal of upgrade tests should not affect the core functionality of package installation and distribution.