minor symfony#20979 [Validator] remove the Slug constraint (xabbuh)

This PR was merged into the 7.3 branch.

Discussion
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[Validator] remove the Slug constraint

fixes symfony#20978

Commits
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e8128a6 remove the Slug constraint

Author: javiereguiluz

reference/constraints/Slug.rst

@@ -33,7 +33,6 @@ String Constraints
 * :doc:`NotCompromisedPassword </reference/constraints/NotCompromisedPassword>`
 * :doc:`PasswordStrength </reference/constraints/PasswordStrength>`
 * :doc:`Regex </reference/constraints/Regex>`
-* :doc:`Slug </reference/constraints/Slug>`
 * :doc:`Twig </reference/constraints/Twig>`
 * :doc:`Ulid </reference/constraints/Ulid>`
 * :doc:`Url </reference/constraints/Url>`