minor #17770 [Validator] Remove annotations from exactly option of Length constraint (alexandre-daubois)

This PR was merged into the 6.0 branch.

Discussion
----------

[Validator] Remove annotations from `exactly` option of Length constraint

Follow-up #17764 (comment)

Commits
-------

13d15fa [Validator] Remove annotations from `exactly` option of Length constraint

Author: OskarStark

reference/constraints/Length.rst

@@ -135,8 +135,7 @@ the given value's length is not **exactly** equal to this value.
 
     This option is the one being set by default when using the Length constraint
     without passing any named argument to it. This means that for example,
-    ``@Assert\Length(20)`` and ``@Assert\Length(exactly=20)`` are equivalent, as
-    well as ``#[Assert\Length(20)]`` and ``#[Assert\Length(exactly: 20)]``.
+    ``#[Assert\Length(20)]`` and ``#[Assert\Length(exactly: 20)]`` are equivalent.
 
 exactMessage
 ~~~~~~~~~~~~