Remove incorrect unparenting guidance from migration guide

This rule is almost always wrong, and we're having some trouble agreeing
on replacement text. Let's remove the whole paragraph for now, to avoid
confusion.

diff --git a/docs/reference/gtk/migrating-3to4.md b/docs/reference/gtk/migrating-3to4.md
index 9112ec2132fdbea8716414358573871180cca923..aa93f4ac1dabd7453c4e95e07dd4df493244ddfb 100644 (file)
--- a/docs/reference/gtk/migrating-3to4.md
+++ b/docs/reference/gtk/migrating-3to4.md
@@ -264,14 +264,6 @@ therefore can no longer be used to break reference cycles. A typical sign
 of a reference cycle involving a toplevel window is when closing the window
 does not make the application quit.
 
-A good rule to follow is: If you set a widget pointer with
-gtk_widget_class_bind_template_child() in class_init(), you need to
-unparent it in dispose(). The slight complication here is that you need
-to respect the widget hierarchy while doing so. Ie if you set both `field1`
-and `field2`, but `field1` is an ancestor of `field2`, then you only need
-to unparent `field1` — doing so will remove the the entire subtree below
-`field1`, including `field2`.
-
 ### Stop using GdkScreen
 
 The GdkScreen object has been removed in GTK 4. Most of its APIs already