Download language server from enterprise portal in enterprise mode.

[fortenforge]

Also bump LS version to 1.6.10

[thedemons]

We also need to delete and re-download the language server when the user switches to enterprise mode:

public async Task PrepareAsync()
{
    string binaryPath = Package.GetLanguageServerPath();
    if (File.Exists(binaryPath))
    {
        await StartAsync();
        return;
    }

One easy way is to modify the GetLanguageServerPath() function to return "language_server_enterprise_windows_x64.exe" or something similar when in enterprise mode.