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.

{ "blockchain",         &getblockheader,                     },
    { "blockchain",         &getchaintips,                       },
    { "blockchain",         &getdifficulty,                      },
    { "blockchain",         &getmempoolancestors,                },
    { "blockchain",         &getmempooldescendants,              },
    { "blockchain",         &getmempoolentry,                    },
    { "blockchain",         &getmempoolinfo,                     },
    { "blockchain",         &getrawmempool,                      },
    { "blockchain",         &gettxout,                           },
    { "blockchain",         &gettxoutsetinfo,                    },
    { "blockchain",         &pruneblockchain,                    },
    { "blockchain",         &savemempool,                        },
    { "blockchain",         &verifychain,                        },
    { "blockchain",         &preciousblock,                      },
    { "blockchain",         &scantxoutset,                       },
    { "blockchain",         &getblockfilter,                     },
    
    { "hidden",              &invalidateblock,                   },
    { "hidden",              &reconsiderblock,                   },
    { "hidden",              &waitfornewblock,                   },
    { "hidden",              &waitforblock,                      },
    { "hidden",              &waitforblockheight,                },
    { "hidden",              &syncwithvalidationinterfacequeue,  },
    { "hidden",              &dumptxoutset,                      },
};
    for (const auto& c : commands) {
        t.appendCommand(c.name, &c);
    }
}