Revert "Make ProjectElementContainers.DeepCopyFrom copy all descendants (dotnet#7454)"

This reverts commit e39a9be.

Fixes a regression caused by the fix, tracked as
https://devdiv.visualstudio.com/DevDiv/_workitems/edit/1526076.

Author: rainersigwald

src/Build.OM.UnitTests/Construction/ProjectItemGroupElement_tests.cs

@@ -5,7 +5,6 @@
 using System.Xml;
 
 using Microsoft.Build.Construction;
-using Shouldly;
 using Xunit;
 
 #nullable disable
@@ -71,49 +70,6 @@ public void ReadItemGroupTwoItems()
             Assert.Equal("i2", items[1].Include);
         }
 
-        [Fact]
-        public void DeepCopyFromItemGroupWithMetadata()
-        {
-            string content = @"
-                    <Project>
-                        <ItemGroup>
-                            <i Include='i1'>
-                              <M>metadataValue</M>
-                            </i>
-                            <i Include='i2'>
-                              <M>
-                                <Some>
-                                    <Xml With='Nesting' />
-                                </Some>
-                              </M>
-                            </i>
-                        </ItemGroup>
-                    </Project>
-                ";
-
-            ProjectRootElement project = ProjectRootElement.Create(XmlReader.Create(new StringReader(content)));
-            ProjectItemGroupElement group = (ProjectItemGroupElement)Helpers.GetFirst(project.Children);
-
-            ProjectRootElement newProject = ProjectRootElement.Create();
-            ProjectItemGroupElement newItemGroup = project.AddItemGroup();
-
-            newItemGroup.DeepCopyFrom(group);
-
-            var items = Helpers.MakeList(newItemGroup.Items);
-
-            items.Count.ShouldBe(2);
-
-            items[0].Include.ShouldBe("i1");
-            ProjectMetadataElement metadataElement = items[0].Metadata.ShouldHaveSingleItem();
-            metadataElement.Name.ShouldBe("M");
-            metadataElement.Value.ShouldBe("metadataValue");
-
-            items[1].Include.ShouldBe("i2");
-            metadataElement = items[1].Metadata.ShouldHaveSingleItem();
-            metadataElement.Name.ShouldBe("M");
-            metadataElement.Value.ShouldBe("<Some><Xml With=\"Nesting\" /></Some>");
-        }
-
         /// <summary>
         /// Set the condition value
         /// </summary>

src/Build/Construction/ProjectElementContainer.cs

@@ -407,46 +407,13 @@ protected internal virtual ProjectElementContainer DeepClone(ProjectRootElement
                 }
                 else
                 {
-                    ProjectElement childClone = child.Clone(clone.ContainingProject);
-                    clone.AppendChild(childClone);
-                    if (childClone.XmlElement is not null)
-                    {
-                        AppendAttributesAndChildren(childClone.XmlElement, child.XmlElement);
-                    }
+                    clone.AppendChild(child.Clone(clone.ContainingProject));
                 }
             }
 
             return clone;
         }
 
-        private void AppendAttributesAndChildren(XmlNode appendTo, XmlNode appendFrom)
-        {
-            appendTo.RemoveAll();
-            // Copy over the attributes from the template element.
-            if (appendFrom.Attributes is not null)
-            {
-                foreach (XmlAttribute attribute in appendFrom.Attributes)
-                {
-                    XmlAttribute attr = appendTo.OwnerDocument.CreateAttribute(attribute.LocalName, attribute.NamespaceURI);
-                    attr.Value = attribute.Value;
-                    appendTo.Attributes.Append(attr);
-                }
-            }
-
-            // If this element has pure text content, copy that over.
-            if (appendFrom.ChildNodes.Count == 1 && appendFrom.FirstChild.NodeType == XmlNodeType.Text)
-            {
-                appendTo.AppendChild(appendTo.OwnerDocument.CreateTextNode(appendFrom.FirstChild.Value));
-            }
-
-            foreach (XmlNode child in appendFrom.ChildNodes)
-            {
-                XmlNode childClone = appendTo.OwnerDocument.CreateNode(child.NodeType, child.Prefix, child.Name, child.NamespaceURI);
-                appendTo.AppendChild(childClone);
-                AppendAttributesAndChildren(childClone, child);
-            }
-        }
-
         internal static ProjectElementContainer DeepClone(ProjectElementContainer xml, ProjectRootElement factory, ProjectElementContainer parent)
         {
             return xml.DeepClone(factory, parent);