Remove obsolete script to archive branches

Apparently, there was a practice to archive branches by tagging them
"archive/branch-name" and then deleting them. We don't practice that
anymore and I would suggest to not start doing it again. Our setup is a
bit different now.

We now use our own forks for feature branches and can have our own,
individual archiving practices in our forks. There is no need to have a
central graveyard of people's "work after progress".

The old feature branches we used to have in the central repository got
archived in another fork:
https://github.com/openfoodfoundation/openfoodnetwork-archive/

Branches associated to pull requests should be deleted after the pull
request has been closed. Github keeps a reference to those branches in
the pull request which is like an archive.

Special branches we still have and delete from time to time:

- transifex: Created for new translations, deleted afterwards.
- dependabot/*: Dependabot always creates pull requests. See above.
- 1-31-1-stable etc: They only live as long as they are supported.

I would also like to delete the old `archive/*` tags. They are in the
openfoodnetwork-archive repository and could confuse developers in the
main repository. Let's keep it clean.

script/archive_branch.sh

@@ -1,10 +0,0 @@
-#!/bin/bash
-
-# Archive an old branch as a tagged named archive/branch-name to declutter the branch list
-
-BRANCH_NAME=$1
-
-git tag archive/$BRANCH_NAME $BRANCH_NAME
-git checkout -q archive/$BRANCH_NAME
-git branch -d $BRANCH_NAME
-git checkout -q master