Bring back legacy proto #11

Job	Run time
Check rustdoc intra-doc links	35s
Cross compile (armv7-unknown-linux-gnueabihf)	11s
Cross compile (powerpc-unknown-linux-gnu)	22s
Clippy	1m 13s
Test Suite	2m 12s
Check	1m 50s
Cross compile (powerpc64-unknown-linux-gnu)	27s
Rustfmt	19s
Cross compile (wasm32-unknown-unknown)	30s
	7m 39s

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