Reverts "TreeSliver & associated classes (flutter#147171)" (flutter#149754)

Reverts: flutter#147171
Initiated by: QuncCccccc
Reason for reverting: tree is red due to a test in this PR
Original PR Author: Piinks

Reviewed By: {QuncCccccc, TahaTesser, bleroux}

This change reverts the following previous change:
**FYI for Reviewers:** Much of the API surface matches that of the 2D TreeView in flutter/packages#6592. If it changes here, it should change there, and vice versa.

📜  [Design Document](https://docs.google.com/document/d/1-aFI7VjkF9yMkWpP94J8T_JREDS-M3bOak26PVehUYg/edit?usp=sharing)

This adds classes and associated callbacks and controllers for TreeSliver. Core components:
- TreeSliver
- RenderTreeSliver
- TreeSliverNode
- TreeSliverController
- TreeSliverStateMixin
- TreeSliverIndentationType

Fixes flutter#114299

https://github.com/flutter/flutter/assets/16964204/3facd095-7262-4068-aa33-d713e2deca99

https://github.com/flutter/flutter/assets/16964204/f851ae30-8e71-45c7-82a4-9606986a5872

Author: auto-submit[bot]

examples/api/lib/widgets/sliver/sliver_tree.0.dart

@@ -67,7 +67,6 @@ export 'src/rendering/sliver_list.dart';
 export 'src/rendering/sliver_multi_box_adaptor.dart';
 export 'src/rendering/sliver_padding.dart';
 export 'src/rendering/sliver_persistent_header.dart';
-export 'src/rendering/sliver_tree.dart';
 export 'src/rendering/stack.dart';
 export 'src/rendering/table.dart';
 export 'src/rendering/table_border.dart';

examples/api/lib/widgets/sliver/sliver_tree.1.dart

@@ -8,7 +8,6 @@ import 'package:vector_math/vector_math_64.dart';
 import 'box.dart';
 import 'object.dart';
 import 'sliver.dart';
-import 'sliver_fixed_extent_list.dart';
 
 /// A delegate used by [RenderSliverMultiBoxAdaptor] to manage its children.
 ///