minor #8260 Delete use_virtuals_forms.rst (afurculita)

This PR was squashed before being merged into the 3.3 branch (closes #8260).

Discussion
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Delete use_virtuals_forms.rst

As this is about an option from Symfony 2 and removed years ago in Symfony 2.3, this can be removed from the docs for Symfony 3

Commits
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4c66f31 Delete use_virtuals_forms.rst

Author: xabbuh

form/use_virtuals_forms.rst

@@ -696,12 +696,6 @@ There's a lot more to learn and a lot of *powerful* tricks in the form system.
 
 Learn more
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-
-.. toctree::
-    :hidden:
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-    form/use_virtuals_forms
-
 .. toctree::
     :maxdepth: 1
     :glob: