Remove old dfbench runner once benchmarks are migrated to the new SQL benchmark framework #24312

Is your feature request related to a problem or challenge?

• Part of [EPIC] Add SQL based benchmarking #21706
• Follow up to CLI (non criterion) interface for sql runner #21937

Most benchmark suites have been ported to the new SQL based benchmark framework (benchmark_runner, see #21707 and follow on PRs). However, the old rust-based dfbench runner (benchmarks/src/bin/dfbench.rs and the per-suite modules in benchmarks/src/) still exists in parallel.

Maintaining two benchmark implementations means duplicated code and the risk that the two runners drift apart and report different results for the same suite.

Describe the solution you'd like

Once bench.sh has been migrated to the new framework (#24311), remove the old dfbench runner and the now-unused suite code, keeping dfbench only for benchmarks that cannot be expressed as SQL (if any remain).

Describe alternatives you've considered

Keep both runners indefinitely.

Additional context

@Omega359 mentioned in #21937 (comment) that they planned to file/work on this cleanup.