minor #17767 [Validator] Remove superfluous versionadded (alexandre-daubois)

This PR was merged into the 6.0 branch.

Discussion
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[Validator] Remove superfluous `versionadded`

This removes a superfluous `versionadded` from 6.0 branch

Commits
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d417467 [Validator] Remove superfluous `versionadded`

Author: OskarStark

reference/constraints/Length.rst

@@ -138,10 +138,6 @@ the given value's length is not **exactly** equal to this value.
     ``@Assert\Length(20)`` and ``@Assert\Length(exactly=20)`` are equivalent, as
     well as ``#[Assert\Length(20)]`` and ``#[Assert\Length(exactly: 20)]``.
 
-.. versionadded:: 5.2
-
-    The named argument ``exactly`` was introduced in Symfony 5.2.
-
 exactMessage
 ~~~~~~~~~~~~