Revert "Fixed leading button size on app bar (#110043)" (#110103)

This reverts commit 7e33cd5e.

packages/flutter/lib/src/material/app_bar.dart

@@ -998,16 +998,11 @@ class _AppBarState extends State<AppBar> {
       }
     }
     if (leading != null) {
-      leading = theme.useMaterial3
-        ? Container(
-          alignment: Alignment.center,
-          constraints: BoxConstraints.tightFor(width: widget.leadingWidth ?? _kLeadingWidth),
-          child: leading,
-        )
-        : ConstrainedBox(
-          constraints: BoxConstraints.tightFor(width: widget.leadingWidth ?? _kLeadingWidth),
-          child: leading,
-        );
+      leading = Container(
+        alignment: Alignment.center,
+        constraints: BoxConstraints.tightFor(width: widget.leadingWidth ?? _kLeadingWidth),
+        child: leading,
+      );
     }
 
     Widget? title = widget.title;

packages/flutter/test/material/app_bar_test.dart

@@ -694,11 +694,9 @@ void main() {
   });
 
   testWidgets('leading button extends to edge and is square', (WidgetTester tester) async {
-    final ThemeData themeData = ThemeData(platform: TargetPlatform.android);
-    final bool material3 = themeData.useMaterial3;
     await tester.pumpWidget(
       MaterialApp(
-        theme: themeData,
+        theme: ThemeData(platform: TargetPlatform.android),
         home: Scaffold(
           appBar: AppBar(
             title: const Text('X'),
@@ -708,9 +706,9 @@ void main() {
       ),
     );
 
-    final Finder hamburger = find.byType(IconButton);
-    expect(tester.getTopLeft(hamburger), material3 ? const Offset(4.0, 4.0) : Offset.zero);
-    expect(tester.getSize(hamburger), material3 ? const Size(48.0, 48.0) : const Size(56.0, 56.0));
+    final Finder hamburger = find.byTooltip('Open navigation menu');
+    expect(tester.getTopLeft(hamburger), const Offset(4.0, 4.0));
+    expect(tester.getSize(hamburger), const Size(48.0, 48.0));
   });
 
   testWidgets('test action is 4dp from edge and 48dp min', (WidgetTester tester) async {