Remove colloquialism "hold on"

I'm of the thought that documentation should balance between conversational grammar and formal grammar. Hold on pushes that over the conversational boundary, in my opinion. Thoughts?

Author: Micheal Cottingham

form/dynamic_form_modification.rst

@@ -32,8 +32,8 @@ take a look at the :doc:`Form Events </form/events>` documentation.
 Customizing your Form Based on the Underlying Data
 --------------------------------------------------
 
-Before jumping right into dynamic form generation, hold on and recall what
-a bare form class looks like::
+Before jumping right into dynamic form generation, recall what
+a bare form class looks like:
 
     // src/AppBundle/Form/Type/ProductType.php
     namespace AppBundle\Form\Type;