signrawtransaction Node RPC being deprecated

[tynes]

From the Bitcoin v0.17.0 Release Notes

signrawtransaction is deprecated and will be fully removed in v0.18.
To use signrawtransaction in v0.17, restart bitcoind with
-deprecatedrpc=signrawtransaction. Projects should transition to
using signrawtransactionwithkey and signrawtransactionwithwallet
before upgrading to v0.18.

This RPC method looks to spend coins that are already in the mempool. See:

bcoin/lib/node/rpc.js

Line 1902 in 01a7156

tx.view = await this.mempool.getSpentView(tx);

I'm not sure if its the most useful RPC method. We should consider deprecating it as well

https://bitcoincore.org/en/doc/0.17.0/rpc/rawtransactions/signrawtransaction/

[braydonf]

As there are separate RPC interfaces for node and wallet in bcoin already, this is pretty much done already. Therefore, having signwithtransactionwithkey and signrawtransactionwithwallet likely isn't a necessary move. Currently signrawtransaction isn't part of the wallet however, and is part of the node.

For the wallet case, air-gapped signing, is where I think this would apply, see #722 which mentions the addition of a wallet command for signing PSBT.