`LaunchProtoData` should clean the output dir only when needed

Now it does all the time:

```kotlin
internal fun setPreLaunchCleanup() {
    doFirst(CleanAction())
}
```
This forces the users always perform `./gradlew clean build`. The `clean` task call is required to invalidate the input for `generateProto` task, which produces the input for `launchProtoData`. Otherwise, we end up with an empty target directory, which, in turn, breaks the compilation.
