Remove a duplicated line

Author: Dinduks

reference/constraints/Email.rst

@@ -9,7 +9,7 @@ cast to a string before being validated.
 +----------------+---------------------------------------------------------------------+
 | Options        | - `message`_                                                        |
 |                | - `checkMX`_                                                        |
-|                | - `checkHost`_                                                        |
+|                | - `checkHost`_                                                      |
 +----------------+---------------------------------------------------------------------+
 | Class          | :class:`Symfony\\Component\\Validator\\Constraints\\Email`          |
 +----------------+---------------------------------------------------------------------+
@@ -84,8 +84,6 @@ checkMX
 If true, then the `checkdnsrr`_ PHP function will be used to check the validity
 of the MX record of the host of the given email.
 
-.. _`checkdnsrr`: http://www.php.net/manual/en/function.checkdnsrr.php
-
 checkHost
 ~~~~~~~~~