remove the label_attr option which is not available in the button type

Author: xabbuh

reference/forms/types/button.rst

@@ -15,7 +15,6 @@ A simple, non-responsive button.
 | Options              | - `attr`_                                                            |
 |                      | - `disabled`_                                                        |
 |                      | - `label`_                                                           |
-|                      | - `label_attr`_                                                      |
 |                      | - `translation_domain`_                                              |
 +----------------------+----------------------------------------------------------------------+
 | Overridden options   | - `auto_initialize`_                                                 |
@@ -34,8 +33,6 @@ Options
 
 .. include:: /reference/forms/types/options/button_label.rst.inc
 
-.. include:: /reference/forms/types/options/label_attr.rst.inc
-
 .. include:: /reference/forms/types/options/button_translation_domain.rst.inc
 
 Overridden Options