minor symfony#13874 Update sessions.rst (atailouloute)

This PR was merged into the 3.4 branch.

Discussion
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Update sessions.rst

Add missing method of `SessionBagInterface`

Commits
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1534b7b Update sessions.rst

Author: javiereguiluz

components/http_foundation/sessions.rst

@@ -151,6 +151,9 @@ the following API which is intended mainly for internal purposes:
 :method:`Symfony\\Component\\HttpFoundation\\Session\\SessionBagInterface::getName`
     Returns the name of the session bag.
 
+:method:`Symfony\\Component\\HttpFoundation\\Session\\SessionBagInterface::clear`
+    Clears out data from bag.
+
 .. _attribute-bag-interface:
 
 Attributes