Remove kanban management github action workflow

This workflow only supports classic projects [1], but we're migrating to
new projects because github will automatically close classic projects on
August 23 [2].

[1] Issue 89 in https://github.com/srggrs/assign-one-project-github-action/
[2] https://github.blog/changelog/2024-05-23-sunset-notice-projects-classic/