Reverts "BoxPainter should dispatch creation and disposal events." (#141545)

Reverts flutter/flutter#141526
Initiated by: CaseyHillers
This change reverts the following previous change:
Original Description:
### Description
- Adds `BoxPainter` creation and disposal events dispatching for memory leak tracking as part of https://github.com/flutter/flutter/issues/141198

### Tests
- Updates `decoration_test.dart` to test `BoxPainter` object creation and disposal events dispatching.

packages/flutter/lib/src/painting/decoration.dart

@@ -198,18 +198,9 @@ abstract class Decoration with Diagnosticable {
 /// happens, the [onChanged] callback will be invoked. To stop this callback
 /// from being called after the painter has been discarded, call [dispose].
 abstract class BoxPainter {
-  /// Default abstract constructor for box painters.
-  BoxPainter([this.onChanged]) {
-    // TODO(polina-c): stop duplicating code across disposables
-    // https://github.com/flutter/flutter/issues/137435
-    if (kFlutterMemoryAllocationsEnabled) {
-      FlutterMemoryAllocations.instance.dispatchObjectCreated(
-        library: 'package:flutter/painting.dart',
-        className: '$BoxPainter',
-        object: this,
-      );
-    }
-  }
+  /// Abstract const constructor. This constructor enables subclasses to provide
+  /// const constructors so that they can be used in const expressions.
+  const BoxPainter([this.onChanged]);
 
   /// Paints the [Decoration] for which this object was created on the
   /// given canvas using the given configuration.
@@ -252,9 +243,5 @@ abstract class BoxPainter {
   /// The [onChanged] callback will not be invoked after this method has been
   /// called.
   @mustCallSuper
-  void dispose() {
-    if (kFlutterMemoryAllocationsEnabled) {
-      FlutterMemoryAllocations.instance.dispatchObjectDisposed(object: this);
-    }
-  }
+  void dispose() { }
 }

packages/flutter/test/painting/decoration_test.dart

@@ -9,7 +9,6 @@ import 'package:fake_async/fake_async.dart';
 import 'package:flutter/foundation.dart';
 import 'package:flutter/painting.dart';
 import 'package:flutter_test/flutter_test.dart';
-import 'package:leak_tracker_flutter_testing/leak_tracker_flutter_testing.dart';
 
 import '../image_data.dart';
 import '../painting/mocks_for_image_cache.dart';
@@ -814,16 +813,4 @@ void main() {
 
     info.dispose();
   }, skip: kIsWeb); // https://github.com/flutter/flutter/issues/87442
-
-  test('$BoxPainter dispatches memory events', () async {
-    await expectLater(
-      await memoryEvents(() => _BoxPainter().dispose(), _BoxPainter),
-      areCreateAndDispose,
-    );
-  });
-}
-
-class _BoxPainter extends BoxPainter {
-  @override
-  void paint(Canvas canvas, Offset offset, ImageConfiguration configuration) {}
 }