Remove "archive courses" feature in separate parts

[TobyCyan]

Duplicate of #11810

Problem Statement

Removal of course archive feature on its own creates one single PR that is too large.

Outline of Solution

• Create 3 separate PRs for the removal in the following order:
• Remove tests -> Remove frontend functionality (disconnect from back-end) -> Remove back-end functionality

[damithc]

@TobyCyan Normally, it's better not to split atomic tasks into multiple PRs, as this causes the code base to go into non-ideal state for a period of time. For example, after removing tests, we end up with a codebase that has untested features.

If the problem is that it is too large to review in one go, the PR can be split into multiple commits, each handling a well-defined part of the task. Then each commit can be reviewed separately. This requires a high level of commit-discipline though.

That said, we can resort to such split PRs of an atomic task in exceptional times -- such as in the middle of a code migration -- and if done within a single iteration/milestone.