Cleanup SemiFutureTest
Cleanup SemiFutureTest

Summary:
- Removed unused EventBase
- Simplified
```
auto f = p.getSemiFuture().toUnsafeFuture();
auto sf = std::move(f).semi().defer(...);
```

to

```
auto sf = p.getSemiFuture().defer(...);
```

- Corrected `semiFutureWithinNoValueReferenceWhenTimeOut`. it wasn't testing anything because the future is not waited for and if it's waited for, `callbackInput` has exception, not value.

Reviewed By: LeeHowes

Differential Revision: D14877386

fbshipit-source-id: 03df59af0339b20aa9e85506640e89cc383f3b9a

facebook/folly,facebook/folly,facebook/folly,facebook/folly,facebook/folly