[#5374] Add deprecation notice in 2.7

Author: wouterj

reference/twig_reference.rst

@@ -104,9 +104,9 @@ asset
     **type**: ``string``
 ``packageName``
     **type**: ``string`` | ``null`` **default**: ``null``
-``absolute``
+``absolute`` (deprecated as of 2.7)
     **type**: ``boolean`` **default**: ``false``
-``version``
+``version`` (deprecated as of 2.7)
     **type**: ``string`` **default** ``null``
 
 Returns a public path to ``path``, which takes into account the base path