Remove redundant info

5.x has only the immutable versions of datetime classes.

en/orm/database-basics.rst

@@ -757,23 +757,6 @@ The above class does a few interesting things:
 Once we've built our custom type, we'll need to :ref:`connect our type
 to our table class <saving-complex-types>`.
 
-.. _immutable-datetime-mapping:
-
-Enabling Immutable DateTime Objects
------------------------------------
-
-Because Date/Time objects are easily mutated in place, CakePHP allows you to
-enable immutable value objects. This is best done in your application's
-**config/bootstrap.php** file::
-
-    TypeFactory::build('datetime')->useImmutable();
-    TypeFactory::build('date')->useImmutable();
-    TypeFactory::build('time')->useImmutable();
-    TypeFactory::build('timestamp')->useImmutable();
-
-.. note::
-    New applications will have immutable objects enabled by default.
-
 Connection Classes
 ==================