Clean up remaining backend strings on the HTML translation linter todolist

What does this MR do?

Part of: #228846 (closed)

Remove direct usage of HTML in translations used in the remaining backend strings so that these strings can be removed from the todolist and translated normally.

Also remove all strings from the todolist that are no longer in the app.

This is a follow up to https://gitlab.com/gitlab-org/gitlab/-/issues/217933 where we disallowed HTML in translations and moved all existing linter errors to a todolist.

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Does this MR meet the acceptance criteria?

Conformity

• Changelog entry
• Documentation (if required)
• Code review guidelines
• Merge request performance guidelines
• Style guides
• Database guides
• Separation of EE specific content

Availability and Testing

• Review and add/update tests for this feature/bug. Consider all test levels. See the Test Planning Process.
• Tested in all supported browsers
• Informed Infrastructure department of a default or new setting change, if applicable per definition of done

Security

If this MR contains changes to processing or storing of credentials or tokens, authorization and authentication methods and other items described in the security review guidelines:

• ~~Label as security and @ mention @gitlab-com/gl-security/appsec~~
• The MR includes necessary changes to maintain consistency between UI, API, email, or other methods
• Security reports checked/validated by a reviewer from the AppSec team