chore: hold the test suite back for a follow-up change

Removes the CI helper scripts, the credential-handling workflow and the
container-pull unit test from this change, and reverts the workflow edits that
existed only to run them. The release asset list is unchanged either way: with
those scripts gone, the original find already yields the same eight shipped
scripts, so that edit is reverted too.

Also points bash_migrate.yml at falcon-linux-migrate.sh. Its current shellcheck
target, cs-migrate.sh, is not in the tree.

Author: carlosmmatos-cs