AG0019 - Do not await what does not need to be awaited

For example in the code below, the `await _service.FetchSomethingAsync()` expression forces compiler to create the state machine that’s behind this feature.

```
public class Something : ISomething
{
readonly IService _service;

public Something(IService service)
{
_service = service;
}

public async Task GetSomethingAsync() => await _service.FetchSomethingAsync();
}
```

It can be easily fixed by

```
public class Something : ISomething
{
readonly IService _service;

public Something(IService service)
{
_service = service;
}

public Task GetSomethingAsync() => _service.FetchSomethingAsync();
}
```

For reference: [Link with measurements](https://www.tabsoverspaces.com/233659-do-not-await-what-does-not-need-to-be-awaited)