[FrameworkBundle] Added UniqueEntity message translation for Spanish

src/Symfony/Bundle/FrameworkBundle/Resources/translations/validators.es.xliff

@@ -162,6 +162,10 @@
                 <source>This value is not a valid country</source>
                 <target>Este valor no es un país válido</target>
             </trans-unit>
+            <trans-unit id="41">
+                <source>This value is already used</source>
+                <target>Este valor ya se ha utilizado</target>
+            </trans-unit>
         </body>
     </file>
 </xliff>