minor #3920 [Components][Form] remove blank line to render the versionadded directive properly (xabbuh)

This PR was submitted for the master branch but it was merged into the 2.3 branch instead (closes #3920).

Discussion
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[Components][Form] remove blank line to render the versionadded directive properly

| Q             | A
| ------------- | ---
| Doc fix?      | yes
| New docs?     | no
| Applies to    | all
| Fixed tickets |

Commits
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7ade4f6 remove blank line to render the versionadded directive properly

Author: weaverryan

components/form/form_events.rst

@@ -257,7 +257,6 @@ processed.
 +------------------------+-------------------------------+------------------+
 
 .. versionadded:: 2.3
-
     Before Symfony 2.3, ``FormEvents::PRE_SUBMIT``, ``FormEvents::SUBMIT``
     and ``FormEvents::POST_SUBMIT`` were called ``FormEvents::PRE_BIND``,
     ``FormEvents::BIND`` and ``FormEvents::POST_BIND``.