Reverts "Introduce AnimationStyle" (#138628)

Reverts flutter/flutter#137945
Initiated by: HansMuller
This change reverts the following previous change:
Original Description:
This PR introduces `AnimationStyle`, it is used to override default animation curves and durations in several widgets.

fixes  [Add the ability to customize MaterialApp theme animation duration](flutter/flutter#78372)
fixes [Allow customization of showMenu transition animation curves and duration](flutter/flutter#135638)

Here is an example where popup menu curve and transition duration is overriden:

```dart
          popUpAnimationStyle: AnimationStyle(
            curve: Easing.emphasizedAccelerate,
            duration: Durations.medium4,
          ),
```

Set `AnimationStyle.noAnimation` to disable animation.
```dart
    return MaterialApp(
      themeAnimationStyle: AnimationStyle.noAnimation,
```

Author: auto-submit[bot]

examples/api/lib/material/app/app.0.dart

@@ -30,18 +30,19 @@ class PopupMenuExample extends StatefulWidget {
 }
 
 class _PopupMenuExampleState extends State<PopupMenuExample> {
-  SampleItem? selectedItem;
+  SampleItem? selectedMenu;
 
   @override
   Widget build(BuildContext context) {
     return Scaffold(
       appBar: AppBar(title: const Text('PopupMenuButton')),
       body: Center(
         child: PopupMenuButton<SampleItem>(
-          initialValue: selectedItem,
+          initialValue: selectedMenu,
+          // Callback that sets the selected popup menu item.
           onSelected: (SampleItem item) {
             setState(() {
-              selectedItem = item;
+              selectedMenu = item;
             });
           },
           itemBuilder: (BuildContext context) => <PopupMenuEntry<SampleItem>>[

examples/api/lib/material/popup_menu/popup_menu.0.dart

@@ -31,18 +31,19 @@ class PopupMenuExample extends StatefulWidget {
 }
 
 class _PopupMenuExampleState extends State<PopupMenuExample> {
-  SampleItem? selectedItem;
+  SampleItem? selectedMenu;
 
   @override
   Widget build(BuildContext context) {
     return Scaffold(
       appBar: AppBar(title: const Text('PopupMenuButton')),
       body: Center(
         child: PopupMenuButton<SampleItem>(
-          initialValue: selectedItem,
+          initialValue: selectedMenu,
+          // Callback that sets the selected popup menu item.
           onSelected: (SampleItem item) {
             setState(() {
-              selectedItem = item;
+              selectedMenu = item;
             });
           },
           itemBuilder: (BuildContext context) => <PopupMenuEntry<SampleItem>>[