Remove code_sharing and place_tracker, cleanup repo (#2831)

Fixes #2818, #2523, #2528

cupertino_gallery/lib/widgets/text_field_page.dart

@@ -6,15 +6,11 @@ class TextFieldPage extends StatelessWidget {
   @override
   Widget build(BuildContext context) {
     return const CupertinoPageScaffold(
-      navigationBar: CupertinoNavigationBar(
-        middle: Text('Text Field'),
-      ),
+      navigationBar: CupertinoNavigationBar(middle: Text('Text Field')),
       child: Center(
         child: Padding(
           padding: EdgeInsets.all(16.0),
-          child: CupertinoTextField(
-            placeholder: 'Enter text',
-          ),
+          child: CupertinoTextField(placeholder: 'Enter text'),
         ),
       ),
     );