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.

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{RPCResult::Type::ARR, "removed", "<structure is the same as \"transactions\" above, only present if include_removed=true>\n"
                            "Note: transactions that were re-added in the active chain will appear as-is in this array, and may thus have a positive confirmation count."
                        , {{RPCResult::Type::ELISION, "", ""},}},
                        {RPCResult::Type::STR_HEX, "lastblock", "The hash of the block (target_confirmations-1) from the best block on the main chain. This is typically used to feed back into listsinceblock the next time you call it. So you would generally use a target_confirmations of say 6, so you will be continually re-notified of transactions until they've reached 6 confirmations plus any new ones"},
                    }
                },
                RPCExamples{
                    HelpExampleCli("listsinceblock", "")
            + HelpExampleCli("listsinceblock", "\"000000000000000bacf66f7497b7dc45ef753ee9a7d38571037cdb1a57f663ad\" 6")
            + HelpExampleRpc("listsinceblock", "\"000000000000000bacf66f7497b7dc45ef753ee9a7d38571037cdb1a57f663ad\", 6")
                },
            }.Check(request);
    
    
    pwallet->BlockUntilSyncedToCurrentChain();
    auto locked_chain = pwallet->chain().lock();
    LOCK(pwallet->cs_wallet);
    
    Optional<int> height = MakeOptional(false, int()); 
    Optional<int> altheight; 
    int target_confirms = 1;
    isminefilter filter = ISMINE_SPENDABLE;
    uint256 blockId;
    if (!request.params[0].isNull() && !request.params[0].get_str().empty()) {
        blockId = ParseHashV(request.params[0], "blockhash");
        height = locked_chain->findFork(blockId, &altheight);
        if (!height) {
            throw JSONRPCError(RPC_INVALID_ADDRESS_OR_KEY, "Block not found");
        }
    }