Do not force users to have Google's LocationService enabled

## 🐛 Bug Report

Having turned on location service with Google's location service turned off (see screenshot), I expect to be able to use the location services provided by the system, not by Google's services.
Unfortunately, it seems, that we are stuck with using Google services, if they are installed with the system.

Also it would be nice, ~to have a hint in the Readme, when and how Google's service is used,~ and to manually configure whether we should force the user to use google's services.

### Expected behavior
In the scenario above, I expect `await Geolocator.isLocationServicesEnabled()` to return true, but it returns false.

### Reproduction steps

- Turn on location service,
- Turn off Google's location service,
- Run `await Geolocator.isLocationServiceEnabled()`.

### Configuration

**Version:** 6.1.13

**Platform:**
- [ ] :iphone: iOS
- [x] :robot: Android


Edit: I noticed, that there is in fact a hint in the readme. :)

Start at the Android implementation of Geolocator.isLocationServicesEnabled() and reproduce the issue using the listed Android steps. Trace how system location and Google's location service are evaluated. Done means the method reports true when system location is enabled even if Google's location service is disabled.

Written by the indexing model from the issue text.