[cleanup] remove unused and orphaned icons

[pq]

Removes 31 unreferenced icon assets including orphaned @2x files from prior cleanup PRs (#8231, #9036) and obsolete legacy service icons (Observatory, memory dashboard, timeline).

(Driven by /cleanup-unused-assets 🎉.)

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[gemini-code-assist]

Code Review

This pull request deletes an SVG graphic file. There are no review comments to evaluate, and I have no feedback to provide.