remove Layer.replaceWith due to no usage and no tests (flutter#33164)

Author: yjbanov

packages/flutter/lib/src/rendering/layer.dart

@@ -125,39 +125,6 @@ abstract class Layer extends AbstractNode with DiagnosticableTreeMixin {
     parent?._removeChild(this);
   }
 
-  /// Replaces this layer with the given layer in the parent layer's child list.
-  void replaceWith(Layer newLayer) {
-    assert(parent != null);
-    assert(attached == parent.attached);
-    assert(newLayer.parent == null);
-    assert(newLayer._nextSibling == null);
-    assert(newLayer._previousSibling == null);
-    assert(!newLayer.attached);
-    newLayer._nextSibling = nextSibling;
-    if (_nextSibling != null)
-      _nextSibling._previousSibling = newLayer;
-    newLayer._previousSibling = previousSibling;
-    if (_previousSibling != null)
-      _previousSibling._nextSibling = newLayer;
-    assert(() {
-      Layer node = this;
-      while (node.parent != null)
-        node = node.parent;
-      assert(node != newLayer); // indicates we are about to create a cycle
-      return true;
-    }());
-    parent.adoptChild(newLayer);
-    assert(newLayer.attached == parent.attached);
-    if (parent.firstChild == this)
-      parent._firstChild = newLayer;
-    if (parent.lastChild == this)
-      parent._lastChild = newLayer;
-    _nextSibling = null;
-    _previousSibling = null;
-    parent.dropChild(this);
-    assert(!attached);
-  }
-
   /// Returns the value of [S] that corresponds to the point described by
   /// [regionOffset].
   ///