android.app.background_running doesn't need to be set for QtService

The manifest attribute android.app.background_running is set for QtActivity to decide whether to allow Qt to continue running in the background or not, and in our documentation and some examples it's being set under services as well, which might not be needed at all because QtServiceLoader doesn't account for it at all.

So, we could fix those instance and remove the need to set that for the services, because their behavior is like it's always set to true.