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.

#include <rpc/server.h>
#include <rpc/util.h>
#include <script/descriptor.h>
#include <streams.h>
#include <sync.h>
#include <txdb.h>
#include <txmempool.h>
#include <undo.h>
#include <util/strencodings.h>
#include <util/string.h>
#include <util/system.h>
#include <util/translation.h>
#include <validation.h>
#include <validationinterface.h>
#include <versionbits.h>
#include <warnings.h>
#include <stdint.h>
#include <univalue.h>
#include <condition_variable>
#include <memory>
#include <mutex>
struct CUpdatedBlock
{
    uint256 hash;
    int height;
};
static Mutex cs_blockchange;
static std::condition_variable cond_blockchange;
static CUpdatedBlock latestblock GUARDED_BY(cs_blockchange);
NodeContext& EnsureAnyNodeContext(const std::any& context)