Remove skrifa from vello's public API #1819

Job	Run time
cargo check (msrv) (wasm32)	1m 30s
cargo check (aarch64-android)	1m 30s
cargo check (msrv) (windows-latest)	3m 27s
cargo clippy (windows-latest)	2m 47s
cargo check (msrv) (macos-latest)	1m 10s
cargo clippy (wasm32)	3m 10s
cargo clippy (macos-latest)	3m 51s
cargo doc	1m 41s
cargo check (msrv) (ubuntu-latest)	1m 42s
cargo clippy (ubuntu-latest)	3m 59s
formatting	20s
Prime LFS Cache	4s
cargo test (wasm32)	1m 29s
typos	5s
cargo test (windows-latest)	3m 55s
cargo test (macos-latest)	4m 23s
cargo test (ubuntu-latest)	4m 30s
	39m 33s

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