Remove vestigal conbench integration #25096

Job	Run time
Check cargo fmt	37s
cargo check	3m 21s
cargo test (macos)	18m 49s
build with wasm-pack	2m 27s
cargo test (macos-aarch64)	11m 58s
Verify Vendored Code	53s
cargo test (win64)	45m 6s
Verify MSRV (Min Supported Rust Version)	6m 37s
cargo doc	3m 51s
cargo test datafusion-cli (amd64)	3m 40s
cargo test doc (amd64)	12m 58s
cargo test (amd64)	10m 25s
check Cargo.toml formatting	2m 59s
cargo examples (amd64)	11m 4s
clippy	6m 10s
check configs.md is up-to-date	2m 51s
cargo test hash collisions (amd64)	9m 56s
Run sqllogictest with Postgres runner	3m 8s
cargo test pyarrow (amd64)	2m 28s
verify benchmark results (amd64)	10m 11s
	2h 49m 29s

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