minor #10901 remove Symfony 2.8 versionadded directive (xabbuh)

This PR was merged into the 3.4 branch.

Discussion
----------

remove Symfony 2.8 versionadded directive

<!--

If your pull request fixes a BUG, use the oldest maintained branch that contains
the bug (see https://symfony.com/roadmap for the list of maintained branches).

If your pull request documents a NEW FEATURE, use the same Symfony branch where
the feature was introduced (and `master` for features of unreleased versions).

-->

Commits
-------

bee45aa remove Symfony 2.8 versionadded directive

Author: javiereguiluz

routing/custom_route_loader.rst

@@ -62,10 +62,6 @@ containing :class:`Symfony\\Component\\Routing\\Route` objects.
 Loading Routes with a Custom Service
 ------------------------------------
 
-.. versionadded:: 2.8
-
-    The option to load routes using Symfony services was introduced in Symfony 2.8.
-
 Using a regular Symfony service is the simplest way to load routes in a
 customized way. It's much easier than creating a full custom route loader, so
 you should always consider this option first.