The RPC docs are now enforced to specify the json type of the args and results at compile time. However, some help texts contain the type twice. (E.g. https://github.com/bitcoin/bitcoin/pull/17809#discussion_r386295217 ). The duplicate type in the description should be removed.

Duplicates can be found with this command:

```sh
git grep --extended-regexp  'RPC.*(ARR|OBJ).*json (array|object)' src/rpc/ src/wallet/rpc*
```

#### Useful skills:

Basic understanding of how to compile and run Bitcoin Core.

#### Want to work on this issue?

The purpose of the `good first issue` label is to highlight which issues are suitable for a new contributor without a deep understanding of the codebase.

You do not need to request permission to start working on this. You are encouraged to comment on the issue if you are planning to work on it. This will help other contributors monitor which issues are actively being addressed and is also an effective way to request assistance if and when you need it.

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

{
    /* Please, avoid using the word "pool" here in the RPC interface or help,
     * as users will undoubtedly confuse it with the other "memory pool"
     */
            RPCHelpMan{"getmemoryinfo",
                "Returns an object containing information about memory usage.\n",
                {
                    {"mode", RPCArg::Type::STR,  "\"stats\"", "determines what kind of information is returned.\n"
            "  - \"stats\" returns general statistics about memory usage in the daemon.\n"
            "  - \"mallocinfo\" returns an XML string describing low-level heap state (only available if compiled with glibc 2.10+)."},
                },
                {
                    RPCResult{"mode \"stats\"",
                        RPCResult::Type::OBJ, "", "",
                        {
                            {RPCResult::Type::OBJ, "locked", "Information about locked memory manager",
                            {
                                {RPCResult::Type::NUM, "used", "Number of bytes used"},
                                {RPCResult::Type::NUM, "free", "Number of bytes available in current arenas"},
                                {RPCResult::Type::NUM, "total", "Total number of bytes managed"},
                                {RPCResult::Type::NUM, "locked", "Amount of bytes that succeeded locking. If this number is smaller than total, locking pages failed at some point and key data could be swapped to disk."},