remove `setTorchState()` from the platform interface

@@ -177,14 +177,7 @@ class MethodChannelMobileScanner extends MobileScannerPlatform {
     await methodChannel.invokeMethod<void>('resetScale');
   }
 
-  @override
-  Future<void> setTorchState(TorchState torchState) async {
-    if (torchState == TorchState.unavailable) {
-      return;
-    }
-
-    await methodChannel.invokeMethod<void>('torch', torchState.rawValue);
-  }
+  // TODO: remove the 'torch' function from native
 
   @override
   Future<void> setZoomScale(double zoomScale) async {

@@ -374,13 +374,10 @@ class MobileScannerController extends ValueNotifier<MobileScannerState> {
       return;
     }
 
-    final TorchState newState =
-        torchState == TorchState.off ? TorchState.on : TorchState.off;
-
-    // Update the torch state to the new state.
+    // Request the torch state to be switched to the opposite state.
     // When the platform has updated the torch state,
     // it will send an update through the torch state event stream.
-    await MobileScannerPlatform.instance.setTorchState(newState);
+    await MobileScannerPlatform.instance.toggleTorch();
   }
 
   /// Update the scan window with the given [window] rectangle.

@@ -67,11 +67,6 @@ abstract class MobileScannerPlatform extends PlatformInterface {
   /// This is only supported on the web.
   void setBarcodeLibraryScriptUrl(String scriptUrl) {}
 
-  /// Set the torch state of the active camera.
-  Future<void> setTorchState(TorchState torchState) {
-    throw UnimplementedError('setTorchState() has not been implemented.');
-  }
-
   /// Set the zoom scale of the camera.
   ///
   /// The [zoomScale] must be between `0.0` and `1.0` (both inclusive).

@@ -236,14 +236,6 @@ class MobileScannerWeb extends MobileScannerPlatform {
   }
 
   @override
-  Future<void> setTorchState(TorchState torchState) {
-    throw UnsupportedError(
-      'Setting the torch state is not supported for video tracks on the web.\n'
-      'See https://developer.mozilla.org/en-US/docs/Web/API/MediaTrackConstraints#instance_properties_of_video_tracks',
-    );
-  }
-
-  @override
   Future<void> setZoomScale(double zoomScale) {
     throw UnsupportedError(
       'Setting the zoom scale is not supported for video tracks on the web.\n'