The `generate` RPC method:
- was introduced in 2010
- is now only used for testing
- reaches across multiple components (wallet, mining)

I propose we remove the wallet `generate` RPC method and update all tests to use the `generatetoaddress` RPC method. We can do this non-invasively in the test framework by adding a `generate` method to `TestNode` so that the individual tests do not need to be updated. We could also add a `generate` alias to the `generatetoaddress` RPC method.

Doing this removes a wallet->server dependency and simplifies the wallet->server interface (#10973).

I'm opening this issue before implementing in case anyone has objections.
{
    std::shared_ptr<CWallet> const wallet = GetWalletForJSONRPCRequest(request);
    CWallet* const pwallet = wallet.get();
    if (!EnsureWalletIsAvailable(pwallet, request.fHelp)) {
        return NullUniValue;
    }
    if (request.fHelp || (request.params.size() > 3 ))
        throw std::runtime_error(
            "getbalance ( \"(dummy)\" minconf include_watchonly )\n"
            "\nReturns the total available balance.\n"
            "The available balance is what the wallet considers currently spendable, and is\n"
            "thus affected by options which limit spendability such as -spendzeroconfchange.\n"
            "\nArguments:\n"
            "1. (dummy)           (string, optional) Remains for backward compatibility. Must be excluded or set to \"*\".\n"
            "2. minconf           (numeric, optional, default=0) Only include transactions confirmed at least this many times.\n"