Remove `ast_new` field from `struct rb_parser_config_struct` #502

Job	Run time
cargo test	38s
cargo clippy	38s
make (yjit-bindgen, To fix: use patch in logs, --with-gcc=clang-12 --enable-yjit=dev)	4m 3s
make (check, RUSTC='rustc +1.58.0', 1.58.0)	8m 55s
make (check, --enable-yjit=dev)	11m 58s
make (check, --enable-yjit=dev, --yjit-call-threshold=1 --yjit-verify-ctx --yjit-code-gc)	26m 12s
make (test-bundled-gems, --enable-yjit=dev)	20m 42s
make (yjit-bench, --enable-yjit=dev, --yjit-stats, true)	5m 38s
YJIT Ubuntu result	1s
	1h 18m 45s

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