minor #12268 Removed non working link (quisse)

This PR was submitted for the master branch but it was merged into the 3.4 branch instead (closes #12268).

Discussion
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Removed non working link

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One can't link to a namespace (or so it seems, I'm not that familiar with the docs format so please correct me if I'm wrong). So it seems to me that the non working link should be removed.

Commits
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552ddab Removed non working link

Author: javiereguiluz

validation.rst

@@ -472,7 +472,7 @@ options can be specified in this way.
 This is purely meant to make the configuration of the most common option of
 a constraint shorter and quicker.
 
-If you're ever unsure of how to specify an option, either check :namespace:`Symfony\\Component\\Validator\\Constraints`
+If you're ever unsure of how to specify an option, either check the namespace `Symfony\\Component\\Validator\\Constraints`
 for the constraint or play it safe by always passing in an array of options
 (the first method shown above).