Remove git submodules in favor of DVC

[nepoche]

No description provided.

[drewstone]

@nepoche any chance you can fix up the test script/fixtures issues? Seems a bunch of repos with this change need it also handled in the test CI script.

[duguorong009]

@drewstone @nepoche
The reason of CI failure is from that the name of original submodule dir(substrate-fixtures) does not match with new one(protocol-substrate-fixtures).
So, it should replace all the lines which have the ../substrate-fixtures/... with new name ../protocol-substrate-fixtures/....
For example: In this line, it should be like

(2, 2, 2) =>  include_bytes!("../../../protocol-substrate-fixtures/vanchor/bn254/x5/2-2-2/verifying_key.bin"),