Remove remaining traces of deprecated StringUtils

Author: pimpreneil

components/security/secure_tools.rst

@@ -1,4 +1,4 @@
-Securely Comparing Strings and Generating Random Numbers
+Securely Generating Random Numbers
 ========================================================
 
 The Symfony Security component comes with a collection of nice utilities

cookbook/security/custom_authentication_provider.rst

@@ -289,14 +289,6 @@ the ``PasswordDigest`` header value matches with the user's password.
     provider for the given token. In the case of multiple providers, the
     authentication manager will then move to the next provider in the list.
 
-.. note::
-
-    The comparison of the expected and the provided digests uses a constant
-    time comparison provided by the
-    :method:`Symfony\\Component\\Security\\Core\\Util\\StringUtils::equals`
-    method of the ``StringUtils`` class. It is used to mitigate possible
-    `timing attacks`_.
-
 The Factory
 -----------