Fix GraphQL removals being labelled as deprecations

What does this MR do?

We were previously describing the GraphQL removals page as being a page of deprecations when linking to it from the main GitLab Deprecations page.

Instead, GraphQL deprecations are listed on the main GitLab Deprecations page, alongside other features that are deprecated.

This MR keeps the REST API deprecations page described a separate document of deprecations because that's accurate. The page it links to are deprecations. The REST API deprecations are documented separately because the REST API versioning doesn't follow GitLab's, and so anything "deprecated" in REST v4 would be removed in v5, but there is no timeframe for v5 at present or ability to say what GitLab version it might happen in.

Whereas GraphQL deprecations are pinned to a particular GitLab version, so we document these within the main Deprecations page.

• Related to !175953 (comment 2266501626)
• Related to #509889 (closed)

Related issues

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