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.
{
    return pwallet && pwallet->IsCrypted()
        ? "\nRequires wallet passphrase to be set with walletpassphrase call."
        : "";
}
bool EnsureWalletIsAvailable(CWallet * const pwallet, bool avoidException)
{
    if (pwallet) return true;
    if (avoidException) return false;
    if (!HasWallets()) {
        throw JSONRPCError(
            RPC_METHOD_NOT_FOUND, "Method not found (wallet method is disabled because no wallet is loaded)");
    }
    throw JSONRPCError(RPC_WALLET_NOT_SPECIFIED,
        "Wallet file not specified (must request wallet RPC through /wallet/<filename> uri-path).");
}
void EnsureWalletIsUnlocked(CWallet * const pwallet)
{
    if (pwallet->IsLocked()) {
        throw JSONRPCError(RPC_WALLET_UNLOCK_NEEDED, "Error: Please enter the wallet passphrase with walletpassphrase first.");
    }
}
static void WalletTxToJSON(const CWalletTx& wtx, UniValue& entry) EXCLUSIVE_LOCKS_REQUIRED(cs_main)
{
    int confirms = wtx.GetDepthInMainChain();
    entry.pushKV("confirmations", confirms);
    if (wtx.IsCoinBase())
        entry.pushKV("generated", true);
    if (confirms > 0)