RPCs that return detailed information about mempool entries (e.g. `getmempoolentry` and `getrawmempool(verbose=True)` include the fields `fee`, `modifiedfee`, `descendantfees`, and `ancestorfees` which were marked as "DEPRECATED" and replaced with a `fees` object field in #12240 (since v0.17).

We should remove these fields, but first, properly deprecate them using `-deprecatedrpc`.

#### Useful skills:

- basic understanding of Bitcoin Core RPC interface

#### Want to work on this issue?

For guidance on contributing, please read [CONTRIBUTING.md](https://github.com/bitcoin/bitcoin/blob/master/CONTRIBUTING.md) before opening your pull request.

{
    CBlockUndo blockUndo;
    if (IsBlockPruned(pblockindex)) {
        throw JSONRPCError(RPC_MISC_ERROR, "Undo data not available (pruned data)");
    }
    if (!UndoReadFromDisk(blockUndo, pblockindex)) {
        throw JSONRPCError(RPC_MISC_ERROR, "Can't read undo data from disk");
    }
    return blockUndo;
}
static RPCHelpMan getblock()
{
    return RPCHelpMan{"getblock",
                "\nIf verbosity is 0, returns a string that is serialized, hex-encoded data for block 'hash'.\n"
                "If verbosity is 1, returns an Object with information about block <hash>.\n"
                "If verbosity is 2, returns an Object with information about block <hash> and information about each transaction.\n"
                "If verbosity is 3, returns an Object with information about block <hash> and information about each transaction, including prevout information for inputs (only for unpruned blocks in the current best chain).\n",
                {
                    {"blockhash", RPCArg::Type::STR_HEX, RPCArg::Optional::NO, "The block hash"},
                    {"verbosity|verbose", RPCArg::Type::NUM, RPCArg::Default{1}, "0 for hex-encoded data, 1 for a json object, and 2 for json object with transaction data"},