Remove deprecated `PlatformMenuBar.body` (#138509)

Part of https://github.com/flutter/flutter/issues/139243

## Description

This removes the `PlatformMenuBar.body` attribute and constructor parameter, since its deprecation period has elapsed.

## Tests
 - No tests were using the deprecated attribute, so no tests were removed.

#FlutterDeprecations

packages/flutter/lib/fix_data/fix_widgets/fix_widgets.yaml

@@ -23,6 +23,27 @@
 #     * ListWheelScrollView: fix_list_wheel_scroll_view.yaml
 version: 1
 transforms:
+  # Changes made in https://github.com/flutter/flutter/pull/138509
+  - title: "Migrate to 'PlatformMenuBar.child'"
+    date: 2023-11-15
+    element:
+      uris: [ 'widgets.dart', 'material.dart', 'cupertino.dart' ]
+      field: 'body'
+      inClass: 'PlatformMenuBar'
+    changes:
+      - kind: 'rename'
+        newName: 'child'
+  - title: "Migrate PlatformMenuBar(body:) to PlatformMenuBar(child:)"
+    date: 2023-11-15
+    element:
+      uris: [ 'widgets.dart', 'material.dart', 'cupertino.dart' ]
+      constructor: ''
+      inClass: 'PlatformMenuBar'
+    changes:
+      - kind: 'renameParameter'
+        oldName: 'body'
+        newName: 'child'
+
   # Changes made in https://github.com/flutter/flutter/pull/123352
   - title: "Migrate to 'rootElement'"
     date: 2023-03-13

packages/flutter/lib/src/widgets/platform_menu_bar.dart

@@ -438,28 +438,13 @@ class PlatformMenuBar extends StatefulWidget with DiagnosticableTreeMixin {
     super.key,
     required this.menus,
     this.child,
-    @Deprecated(
-      'Use the child attribute instead. '
-      'This feature was deprecated after v3.1.0-0.0.pre.'
-    )
-    this.body,
-  }) : assert(body == null || child == null,
-              'The body argument is deprecated, and only one of body or child may be used.');
+  });
 
   /// The widget below this widget in the tree.
   ///
   /// {@macro flutter.widgets.ProxyWidget.child}
   final Widget? child;
 
-  /// The widget below this widget in the tree.
-  ///
-  /// This attribute is deprecated, use [child] instead.
-  @Deprecated(
-    'Use the child attribute instead. '
-    'This feature was deprecated after v3.1.0-0.0.pre.'
-  )
-  final Widget? body;
-
   /// The list of menu items that are the top level children of the
   /// [PlatformMenuBar].
   ///
@@ -530,7 +515,7 @@ class _PlatformMenuBarState extends State<PlatformMenuBar> {
   Widget build(BuildContext context) {
     // PlatformMenuBar is really about managing the platform menu bar, and
     // doesn't do any rendering or event handling in Flutter.
-    return widget.child ?? widget.body ?? const SizedBox();
+    return widget.child ?? const SizedBox();
   }
 }
 

packages/flutter/test_fixes/cupertino/cupertino.dart

@@ -245,4 +245,7 @@ void main() {
     clipBehavior: Clip.none,
   );
   final Clip clip = details.clipBehavior;
+
+  final PlatformMenuBar platformMenuBar = PlatformMenuBar(menus: <PlatformMenuItem>[], body: const SizedBox());
+  final Widget bodyValue = platformMenuBar.body;
 }

packages/flutter/test_fixes/cupertino/cupertino.dart.expect

@@ -245,4 +245,7 @@ void main() {
     decorationClipBehavior: Clip.none,
   );
   final Clip clip = details.decorationClipBehavior;
+
+  final PlatformMenuBar platformMenuBar = PlatformMenuBar(menus: <PlatformMenuItem>[], child: const SizedBox());
+  final Widget bodyValue = platformMenuBar.child;
 }

packages/flutter/test_fixes/material/material.dart

@@ -323,4 +323,7 @@ void main() {
   // const Curve curve = standardEasing; expect Easing.legacy
   // const Curve curve = accelerateEasing; expect Easing.legacyAccelerate
   // const Curve curve = decelerateEasing; expect Easing.legacyDecelerate
+
+  final PlatformMenuBar platformMenuBar = PlatformMenuBar(menus: <PlatformMenuItem>[], body: const SizedBox());
+  final Widget bodyValue = platformMenuBar.body;
 }

packages/flutter/test_fixes/material/material.dart.expect

@@ -319,4 +319,7 @@ void main() {
   // const Curve curve = standardEasing; expect Easing.legacy
   // const Curve curve = accelerateEasing; expect Easing.legacyAccelerate
   // const Curve curve = decelerateEasing; expect Easing.legacyDecelerate
+
+  final PlatformMenuBar platformMenuBar = PlatformMenuBar(menus: <PlatformMenuItem>[], child: const SizedBox());
+  final Widget bodyValue = platformMenuBar.child;
 }

packages/flutter/test_fixes/widgets/widgets.dart

@@ -170,4 +170,7 @@ void main() {
     clipBehavior: Clip.none,
   );
   final Clip clip = details.clipBehavior;
+
+  final PlatformMenuBar platformMenuBar = PlatformMenuBar(menus: <PlatformMenuItem>[], body: const SizedBox());
+  final Widget bodyValue = platformMenuBar.body;
 }

packages/flutter/test_fixes/widgets/widgets.dart.expect

@@ -170,4 +170,7 @@ void main() {
     decorationClipBehavior: Clip.none,
   );
   final Clip clip = details.decorationClipBehavior;
+
+  final PlatformMenuBar platformMenuBar = PlatformMenuBar(menus: <PlatformMenuItem>[], child: const SizedBox());
+  final Widget bodyValue = platformMenuBar.child;
 }