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.
{
    if (request.fHelp || request.params.size() < 1 || request.params.size() > 2)
        throw std::runtime_error(
            "estimatesmartfee conf_target (\"estimate_mode\")\n"
            "\nEstimates the approximate fee per kilobyte needed for a transaction to begin\n"
            "confirmation within conf_target blocks if possible and return the number of blocks\n"
            "for which the estimate is valid. Uses virtual transaction size as defined\n"
            "in BIP 141 (witness data is discounted).\n"
            "\nArguments:\n"
            "1. conf_target     (numeric) Confirmation target in blocks (1 - 1008)\n"
            "2. \"estimate_mode\" (string, optional, default=CONSERVATIVE) The fee estimate mode.\n"
            "                   Whether to return a more conservative estimate which also satisfies\n"
            "                   a longer history. A conservative estimate potentially returns a\n"
            "                   higher feerate and is more likely to be sufficient for the desired\n"
            "                   target, but is not as responsive to short term drops in the\n"
            "                   prevailing fee market.  Must be one of:\n"
            "       \"UNSET\"\n"
            "       \"ECONOMICAL\"\n"
            "       \"CONSERVATIVE\"\n"
            "\nResult:\n"
            "{\n"
            "  \"feerate\" : x.x,     (numeric, optional) estimate fee rate in " + CURRENCY_UNIT + "/kB\n"
            "  \"errors\": [ str... ] (json array of strings, optional) Errors encountered during processing\n"
            "  \"blocks\" : n         (numeric) block number where estimate was found\n"
            "}\n"
            "\n"
            "The request target will be clamped between 2 and the highest target\n"
            "fee estimation is able to return based on how long it has been running.\n"