cli: fix -getinfo output when compiled with no wallet

Summary:
Remove null wallet related fields in the output of -getinfo when compiled with no wallet.

This is a backport of Core PR17368

Test Plan:

cmake .. -GNinja -DBUILD_BITCOIN_WALLET=OFF
ninja
src/bitcoind

src/bitcoin-cli -getinfo

The ouput does not show wallet specific fields, such as walletversion, balance, etc

Reviewers: O1 Bitcoin ABC, #bitcoin_abc, Fabien

Reviewed By: O1 Bitcoin ABC, #bitcoin_abc, Fabien

Subscribers: Fabien

Differential Revision: https://reviews.bitcoinabc.org/D8258