Don't clear TemplatedParent on removal from logical tree.

This meant that if a control with a template was removed, when it gets
re-added all of the template children's bindings are broken. The logic
to clear the TemplatedParent when applying a new template is in
TemplatedControl.ApplyTemplate - this is where it should be done.

src/Avalonia.Controls/Control.cs

@@ -721,7 +721,6 @@ namespace Avalonia.Controls
 
                 _isAttachedToLogicalTree = false;
                 _styleDetach.OnNext(this);
-                this.TemplatedParent = null;
                 OnDetachedFromLogicalTree(e);
 
                 foreach (var child in LogicalChildren.OfType<Control>())