"--priv_key_type composite" is not supported

[torao]

Summary of Bug

The simd help says that --priv_key_type composite is available.

--priv_key_type ed25519   specify validator's private key type (ed25519|composite).
                          set this to priv_key.type in priv_validator_key.json; default ed25519 (default "ed25519")

But an error occurs when I do an init with this key specified.

% ./build/simd init Alice --home ./alice --chain-id abc --priv_key_type composite
Error: cannot convert &{sign_key:<bls12:"\253\326\352 ^|$\355<\230\364\264M\210\005\256\351\304\364C\200^*o\253\033\300Fzf\177\362\007\316\004\010c\315\335\225\241\220I\217\014\332!\241" > vrf_key:<ed25519:"a\313l=S\311Ij\024\222h\232\355^\300.\260\003\034\025+=\326\313\t\372\227\354M1;\275" > } from Ostracon public key: invalid type

This is because the key generation and saving it to priv_validator.json is successful, but the decoding when reading the public key doesn't support composite type keys:

https://github.com/line/lbm-sdk/blob/main/crypto/codec/oc.go#L14-L28

Similarly, there appears to be no key implementation for composite.

https://github.com/line/lbm-sdk/tree/main/crypto/keys

It should be fixed so that the composite-key type can be used without error according to the help. Or, it should be clarified that it's not supported now and be fixed that the composite-key type cannot be specified.

Version

% simd version
0.46.0-rc2-287-g8679ec2425

Steps to Reproduce

% make build
% ./build/simd init Alice --home ./alice --chain-id abc --priv_key_type composite

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[zemyblue]

As I know, the composite type is used to use BLS signature. But the BLS signature is in experimental for now. So I think it's good that lbm-sdk doesn't support it yet.

[torao]

Understood. So, for now, the BLS signature aggregation feature is only for experimental use with Ostacon, and the lbm-sdk CLI will not support it now.

Therefore, we need to modify the CLI option included in lbm-sdk to refuse to specify --priv_key_type composite.

1. Remove messages from the help of lbm-sdk CLI so that composite can be used.
2. Remove composite support implementation from --priv_key_type specification in lbm-sdk CLI options.