Remove skrifa from vello's public API #1875

Job	Run time
cargo check (msrv) (wasm32)	54s
cargo check (msrv) (windows-latest)	2m 13s
cargo check (aarch64-android)	38s
cargo check (msrv) (macos-latest)	53s
cargo check (msrv) (ubuntu-latest)	1m 9s
cargo clippy (windows-latest)	3m 41s
cargo clippy (wasm32)	1m 47s
cargo clippy (macos-latest)	1m 31s
cargo doc	1m 40s
cargo clippy (ubuntu-latest)	1m 37s
formatting	13s
Prime LFS Cache	7s
cargo test (wasm32)	47s
typos	4s
cargo test (windows-latest)	2m 43s
cargo test (macos-latest)	1m 45s
cargo test (ubuntu-latest)	4m 12s
	25m 54s

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