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.

{
    return RPCHelpMan{"getchaintips",
                "Return information about all known tips in the block tree,"
                " including the main chain as well as orphaned branches.\n",
                {},
                RPCResult{
                    RPCResult::Type::ARR, "", "",
                    {{RPCResult::Type::OBJ, "", "",
                        {
                            {RPCResult::Type::NUM, "height", "height of the chain tip"},
                            {RPCResult::Type::STR_HEX, "hash", "block hash of the tip"},
                            {RPCResult::Type::NUM, "branchlen", "zero for main chain, otherwise length of branch connecting the tip to the main chain"},
                            {RPCResult::Type::STR, "status", "status of the chain, \"active\" for the main chain\n"
            "Possible values for status:\n"
            "1.  \"invalid\"               This branch contains at least one invalid block\n"
            "2.  \"headers-only\"          Not all blocks for this branch are available, but the headers are valid\n"
            "3.  \"valid-headers\"         All blocks are available for this branch, but they were never fully validated\n"
            "4.  \"valid-fork\"            This branch is not part of the active chain, but is fully validated\n"
            "5.  \"active\"                This is the tip of the active main chain, which is certainly valid"},
                        }}}},
                RPCExamples{
                    HelpExampleCli("getchaintips", "")
            + HelpExampleRpc("getchaintips", "")
                },
        [&](const RPCHelpMan& self, const JSONRPCRequest& request) -> UniValue
{
    ChainstateManager& chainman = EnsureAnyChainman(request.context);
    LOCK(cs_main);