Refine documentation in common_subexpr_eliminate.rs #22

Job	Run time
cargo check	4m 6s
build with wasm-pack	2m 21s
cargo test (macos-aarch64)	10m 53s
cargo test (macos)	26m 48s
Verify Vendored Code	1m 0s
cargo test (win64)	43m 54s
Check cargo fmt	49s
Verify MSRV (Min Supported Rust Version)	7m 37s
cargo test datafusion-cli (amd64)	3m 42s
cargo test doc (amd64)	13m 34s
cargo examples (amd64)	10m 45s
cargo doc	3m 58s
verify benchmark results (amd64)	10m 59s
cargo test (amd64)	10m 42s
check Cargo.toml formatting	3m 14s
clippy	6m 11s
check configs.md is up-to-date	2m 56s
cargo test hash collisions (amd64)	10m 23s
Run sqllogictest with Postgres runner	3m 14s
cargo test pyarrow (amd64)	2m 49s
	2h 59m 55s

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