[#5468] remove outdated warning

cookbook/templating/namespaced_paths.rst

@@ -71,13 +71,6 @@ directory:
             );
         ));
 
-.. caution::
-
-    Prior to 2.8, templates in custom namespaces are not pre-compiled by
-    Symfony's cache warmup process. They are compiled on demand. This may
-    cause problems if two simultaneous requests are trying to use the
-    template for the first time.
-
 The registered namespace is called ``foo_bar``, which refers to the
 ``vendor/acme/foo-bar/templates`` directory. Assuming there's a file
 called ``sidebar.twig`` in that directory, you can use it easily: