As of Gravity Forms 2.4, this functionality is part of the Form Editor and the hook has been deprecated.
This filter is used to enable the inclusion of the hidden choice in the Field Label Visibility and Sub-Label Placement settings on the field Appearance tab in the form editor.
Please bear in mind that hiding the field label will impact the accessibility of your form for users with visual impairments.
add_filter( 'gform_enable_field_label_visibility_settings', '__return_true' );
This hook has no parameters.
This code should be placed in the functions.php file of your active theme.
This filter is located in GFFormDetail::forms_page() in form_detail.php