Revert "Document clean chain behavior for ActiveRecord scope"

guides/source/active_record_querying.md

@@ -2035,61 +2035,6 @@ SELECT books.* FROM books WHERE books.out_of_print = true
 
 [`unscoped`]: https://api.rubyonrails.org/classes/ActiveRecord/Scoping/Default/ClassMethods.html#method-i-unscoped
 
-### New Chains Inside Scope Block
-
-Unlike class methods, [`scope`][] can easily start a new clean chain against the
-model it is defined on.
-
-```ruby
-class Topic < ApplicationRecord
-  scope :toplevel, -> { where(parent_id: nil) }
-  scope :children, -> { where.not(parent_id: nil) }
-  scope :has_children, -> {
-    where(id: Topic.children.select(:parent_id))
-  }
-end
-
-Topic.toplevel.has_children
-```
-
-Inside `has_children` the `Topic` chain generates a subquery like this:
-
-```sql
-SELECT "topics"."parent_id" FROM "topics" WHERE "topics"."parent_id" IS NOT NULL
-```
-
-Class methods have different behavior which can be surprising if you expect them
-to work exactly like scopes.
-
-```ruby
-class Topic < ApplicationRecord
-  def self.toplevel
-    where(parent_id: nil)
-  end
-
-  def self.children
-    where.not(parent_id: nil)
-  end
-
-  def self.has_children
-    where(id: Topic.children.select(:parent_id))
-  end
-end
-
-Topic.toplevel.has_children
-```
-
-`Topic` inside `has_children` will implicitly include `toplevel` from the outer
-chain resulting in a subquery of:
-
-```sql
-SELECT "topics"."parent_id" FROM "topics" WHERE "topics"."parent_id" IS NULL AND "topics"."parent_id" IS NOT NULL
-```
-
-NOTE: In class methods, `self` refers back to the model. In scope, `self` acts as
-a chained relation. For the example above, `self` and `Topic` are interchangeable
-within the class method definition.
-
 Dynamic Finders
 ---------------