Separate benchmark browser follow-up from #982

[helly25]

Restore the merged benchmark workflow change to its intended scope by removing the benchmark-browser UI follow-up that was accidentally included in PR #982. This returns the six affected browser and documentation files exactly to their pre-browser state while retaining all local backfill, upload, dataset, and fixture-design work from #982.

The browser improvements are preserved separately and will be proposed from a dedicated follow-up branch after this correction lands.

AG;DR

• Revert commits 71e13724c0 and afd0e0d4eb, which added and formatted the benchmark-browser card changes.
• Retain commits e347000f91 and cb2d0b92a3, which are the intended benchmark workflow and fixture-design scope of Improve local benchmark backfill and upload workflow #982.
• Limit the correction to:
  • docs/benchmark-comparisons.md
  • tools/benchmark_landscape.py
  • tools/benchmark_landscape_test.py
  • tools/benchmark_web/history.js
  • tools/benchmark_web/landscape.js
  • tools/benchmark_web/landscape.test.mjs
• Verify those six paths exactly match the tree at cb2d0b92a3, immediately before the browser follow-up commits.
• Do not change retained benchmark data, upload behavior, dataset identity, collection behavior, or the versioned-layout design.

Validation:

• bazel test //tools:benchmark_landscape_test
• Changed-file pre-commit hooks
• git diff --check

Known limitation: the already-merged history of #982 cannot be rewritten safely. This corrective change restores main semantically; the browser work will then have its own reviewable PR and history.

[helly25]

Closing: no corrective revert is needed; #982's merged state remains the forward baseline.