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)
        throw std::runtime_error(
            "loadwallet \"filename\"\n"
            "\nLoads a wallet from a wallet file or directory."
            "\nNote that all wallet command-line options used when starting bitcoind will be"
            "\napplied to the new wallet (eg -zapwallettxes, upgradewallet, rescan, etc).\n"
            "\nArguments:\n"
            "1. \"filename\"    (string, required) The wallet directory or .dat file.\n"
            "\nResult:\n"
            "{\n"
            "  \"name\" :    <wallet_name>,        (string) The wallet name if loaded successfully.\n"
            "  \"warning\" : <warning>,            (string) Warning message if wallet was not loaded cleanly.\n"
            "}\n"
            "\nExamples:\n"
            + HelpExampleCli("loadwallet", "\"test.dat\"")