Draft: Remove backup and restore tests

What does this MR do?

For the moment at least, this is experimental/exploratory. See the notes below for related discussions.

Removes the backup and restore tests.

Related to #5178

Related to &37 (comment 1694708113)

As referenced in the links above, our tests have some overlap with upstream tests, but they are not exactly the same. As a result, our pipelines break if changes to the backup and restore process change upstream. This can block releases.

Additionally, our process restores from a static, hand-generated backup from a previous version of GitLab. This is not officially supported, and therefore does not follow the process that an end user should be following.

To summarize this comment, we did indeed catch some regressions in Charts CI thanks to these tests. However, catching them in the Charts CI is arguably too late in the development chain and these tests should be "shifted left" closer to their source code. This is also related to gitlab-org&11635, where we're looking into consolidating backups into a single source where testing and validation can be concentrated.

Related issues

Author checklist

See Definition of done.

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Required

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Expected (please provide an explanation if not completing)

• Test plan indicating conditions for success has been posted and passes
• Documentation created/updated
• Tests added/updated
• Integration tests added to GitLab QA
• Equivalent MR/issue for omnibus-gitlab opened
• Equivalent MR/issue for Gitlab Operator project opened (see Operator documentation on impact of Charts changes)
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