refactor(mobile): tidy-up dependencies, remove unused, replace rarely used ones (#948)

mobile/lib/modules/asset_viewer/ui/download_loading_indicator.dart

@@ -1,24 +0,0 @@
-import 'package:flutter/material.dart';
-import 'package:flutter_spinkit/flutter_spinkit.dart';
-
-class DownloadLoadingIndicator extends StatelessWidget {
-  const DownloadLoadingIndicator({
-    Key? key,
-  }) : super(key: key);
-
-  @override
-  Widget build(BuildContext context) {
-    return Container(
-      height: 60,
-      width: 60,
-      decoration: BoxDecoration(
-        color: Theme.of(context).primaryColor,
-        borderRadius: BorderRadius.circular(10),
-      ),
-      child: const SpinKitDancingSquare(
-        color: Colors.white,
-        size: 30.0,
-      ),
-    );
-  }
-}