Remove deprecated and unused FileSinkExec type #320

Job	Run time
cargo test (macos)	12m 24s
Check cargo fmt	42s
build with wasm-pack	2m 52s
cargo check	11m 28s
cargo test (macos-aarch64)	11m 5s
Verify MSRV (Min Supported Rust Version)	9m 9s
Verify Vendored Code	54s
cargo test (win64)	1h 8m 17s
check configs.md and ***_functions.md is up-to-date	3m 15s
clippy	5m 46s
cargo test hash collisions (amd64)	17m 26s
check Cargo.toml formatting	2m 51s
cargo doc	4m 21s
cargo test (amd64)	11m 41s
cargo test datafusion-cli (amd64)	4m 6s
cargo test doc (amd64)	16m 5s
cargo examples (amd64)	13m 56s
Run sqllogictest with Postgres runner	3m 43s
cargo test pyarrow (amd64)	3m 37s
verify benchmark results (amd64)	13m 9s
	3h 36m 47s

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