rpc: allow pruning of json encoded txs

[cryptochangements34]

Currently if "prune":true and "decode_as_json":true are passed to get_transactions then the hex encoded blob data for the transaction is pruned but the json encoded transaction is not. In this PR, prune rctsig_prunable data from json encoded transaction data returned by get_transactions if "prune":true

[moneromooo-monero]

I think that should probably be removed, since the idea was to include the tx as json, but it's only returned as a string representation anyway, so it's not super useful (and nothing in monero uses it anyway).

[cryptochangements34]

You want to remove the json encoded response all together? Even if it's not "truly json" and it's not used by the core Monero software, I personally find it very useful and since it's an optional response I don't see the harm done in keeping it.

[moneromooo-monero]

Yes, that's what I meant.
If you find it useful, then I guess it's OK to leave it in until we find a way to embed it directly.
Can't you use obj_to_json_str for the pruned tx ?

[cryptochangements34]

When I tried that I got [RPC0] ERROR net src/cryptonote_basic/cryptonote_format_utils.h:181 obj_to_json_str failed: serialization::serialize returned false and whatever would be needed to fix that would probably require a more intrusive patch 🤷‍♂️