Add documentation of all CSS variables available

docs/documentation/form/general.html

@@ -1108,14 +1108,3 @@ variables_keys:
   folder='utilities'
   file='controls'
 %}
-
-{%
-  include docs/components/variables.html
-  anchor_name='Form variables'
-  type='element'
-  variables_keys=page.variables_keys
-  folder='elements'
-  file='form'
-  hide_anchor=true
-  hide_content=true
-%}