Draft: AR delete surface: Remove the client delete-file method

What does this MR do and why?

This MR removes ArtifactRegistry::Client#delete_file, which has no caller in the monolith, along with its spec and a stale comment reference. It touches two files: ee/lib/artifact_registry/client.rb (removes the method, and rewords the comment above #delete_version that previously described both methods) and ee/spec/lib/artifact_registry/client_spec.rb (removes the describe '#delete_file' block).

The method was added in Step 1 ahead of a GraphQL mutation that was going to call it. That mutation has now been dropped from Step 6, following the product design decision that the UI should not offer per-file delete: removing a single file such as a .pom while keeping the .jar corrupts the version for consumers.

Whether Artifact Registry keeps its own delete-file REST route is a separate open question the designer raised with product, and it is not decided or affected by this MR.

No caller exists in the monolith, so nothing else breaks.

References

• Designer's confirmation that the UI should not offer per-file delete: gitlab-org/ops/artifact-registry!2201 (comment 3779379507)
• Reviewer's original question about per-file delete: gitlab-org/ops/artifact-registry!2201 (comment 3773665009)
• Design truth doc, "Format data model: files, versions, tags, deletes": https://gitlab.com/gitlab-org/ci-cd/package-stage/unified-artifact-management/-/blob/main/design/design-truth.md#format-data-model--files-versions-tags-deletes
• Step 1, added #delete_version and #delete_file to the client: !253251 (merged)
• Step 6, added the ArtifactRegistryVersionDelete mutation (originally also included the file delete mutation): !253537 (merged)
• Plan MR, "monolith artifact delete surface": gitlab-org/ops/artifact-registry!2201 (merged)
• Parent scoping issue: #627172
• Epic: &21052

Screenshots or screen recordings

Not applicable. This is a backend-only change with no user-facing surface.

How to set up and validate locally

bundle exec rspec ee/spec/lib/artifact_registry/client_spec.rb
# 819 examples, 0 failures

bundle exec rubocop ee/lib/artifact_registry/client.rb ee/spec/lib/artifact_registry/client_spec.rb
# no offenses detected

A repo-wide search for delete_file finds no remaining Artifact Registry caller.

MR acceptance checklist

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