MDL-82460 form: Remove adv icon from _advancedHTML

The "adv" icon was used in _advancedHTML but was not displayed anywhere,
so it has been deprecated to clean up the code.

lang/en/deprecated.txt

@@ -143,4 +143,5 @@ generalquestionbank,core_backup
 cannotdeletecategoryquestions,core_error
 errordeletingquestionsfromcategory,core_question
 importantupdates_content,core_admin
-importantupdates_title,core_admin
+importantupdates_title,core_admin
+advancedelement,core_form

lang/en/form.php

@@ -24,7 +24,6 @@
  */
 
 $string['addfields'] = 'Add {$a} field(s) to form';
-$string['advancedelement'] = 'Advanced element';
 $string['close'] = 'Close';
 $string['custom'] = 'Custom';
 $string['day'] = 'Day';
@@ -91,3 +90,6 @@ $string['timing'] = 'Timing';
 $string['togglesensitive'] = 'Toggle sensitive';
 $string['unmaskpassword'] = 'Unmask';
 $string['year'] = 'Year';
+
+// Deprecated since Moodle 5.0.
+$string['advancedelement'] = 'Advanced element';

lib/formslib.php

@@ -1775,7 +1775,7 @@ class MoodleQuickForm extends HTML_QuickForm_DHTMLRulesTableless {
             $this->updateAttributes(array('class'=>'mform'));
         }
         $this->_reqHTML = '<span class="req">' . $OUTPUT->pix_icon('req', get_string('requiredelement', 'form')) . '</span>';
-        $this->_advancedHTML = '<span class="adv">' . $OUTPUT->pix_icon('adv', get_string('advancedelement', 'form')) . '</span>';
+        $this->_advancedHTML = '<span class="adv"></span>';
         $this->setRequiredNote(get_string('somefieldsrequired', 'form', $OUTPUT->pix_icon('req', get_string('requiredelement', 'form'))));
     }