minor #6624 remove versionadded directive for 2.x features (xabbuh)

This PR was merged into the 3.0 branch.

Discussion
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remove versionadded directive for 2.x features

Commits
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96dbba8 remove versionadded directive for 2.x features

Author: xabbuh

components/yaml/introduction.rst

@@ -130,9 +130,6 @@ error occurred:
 Objects for Mappings
 ....................
 
-.. versionadded:: 2.7
-    Support for parsing mappings as objects was introduced in Symfony 2.7.
-
 Yaml :ref:`mappings <yaml-format-collections>` are basically associative
 arrays. You can instruct the parser to return mappings as objects (i.e.
 ``\stdClass`` instances) by setting the fourth argument to ``true``::

reference/forms/types/entity.rst

@@ -211,9 +211,6 @@ Overridden Options
 choice_name
 ~~~~~~~~~~~
 
-.. versionadded:: 2.7
-    The ``choice_name`` option was introduced in Symfony 2.7.
-
 **type**: ``string``, ``callable`` or :class:`Symfony\\Component\\PropertyAccess\\PropertyPath` **default**: id
 
 By default the name of each field is the id of the entity, if it can be read
@@ -223,9 +220,6 @@ fall back to using increasing integers.
 choice_value
 ~~~~~~~~~~~~
 
-.. versionadded:: 2.7
-    The ``choice_value`` option was introduced in Symfony 2.7.
-
 **type**: ``string``, ``callable`` or :class:`Symfony\\Component\\PropertyAccess\\PropertyPath` **default**: id
 
 As for the ``choice_name`` option, ``choice_value`` uses the id by default.