write a new method to be accessed from delete_all

The delete method is very coupled with delete all even
though only a portion of the conditionals apply. Decoupling
this will make the code easier to understand and manipulate.

activerecord/lib/active_record/associations/collection_association.rb

@@ -194,7 +194,7 @@ def delete_all(dependent = nil)
                       options[:dependent]
                     end
 
-        delete(:all, dependent: dependent).tap do
+        delete_all_with_dependency(dependent).tap do
           reset
           loaded!
         end
@@ -259,6 +259,14 @@ def delete(*records)
         end
       end
 
+      def delete_all_with_dependency(dependent)
+        if (loaded? || dependent == :destroy) && dependent != :delete_all
+          delete_or_destroy(load_target, dependent)
+        else
+          delete_records(:all, dependent)
+        end
+      end
+
       # Deletes the +records+ and removes them from this association calling
       # +before_remove+ , +after_remove+ , +before_destroy+ and +after_destroy+ callbacks.
       #