chore: Remove redundant assert_starts_with test helper #35291

Job	Run time
Check License Header	2m 10s
cargo check	12m 49s
build with wasm-pack	3m 4s
cargo test (macos)	11m 3s
cargo test (macos-aarch64)	11m 46s
cargo test (win64)	1h 14m 52s
Check cargo fmt	35s
Verify MSRV (Min Supported Rust Version)	9m 15s
Verify Vendored Code	45s
cargo test (amd64)	11m 54s
cargo test datafusion-cli (amd64)	4m 22s
cargo doc	4m 55s
clippy	6m 30s
cargo test doc (amd64)	16m 47s
cargo examples (amd64)	14m 37s
Run sqllogictest with Postgres runner	3m 42s
cargo test pyarrow (amd64)	3m 7s
verify benchmark results (amd64)	13m 25s
check Cargo.toml formatting	2m 58s
check configs.md and ***_functions.md is up-to-date	3m 0s
cargo test hash collisions (amd64)	28m 22s
	3h 59m 58s

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