Update form_collections.rst

See symfony#13439 (comment)

Author: ThomasLandauer

form/form_collections.rst

@@ -11,8 +11,7 @@ that Task, right inside the same form.
 
 .. note::
 
-    The example presented here is based on Doctrine. However, if you're not
-    using Doctrine, it's all very similar.
+    The example presented here is based on Doctrine.
 
 First, suppose that each ``Task`` belongs to multiple ``Tag`` objects. Start
 by creating a simple ``Task`` class::