lib: Remove `HelpText' form element decorator

Zend already has a `Description' decorator.

refs #5525

library/Icinga/Web/Form/Decorator/HelpText.php

@@ -1,37 +0,0 @@
-<?php
-// {{{ICINGA_LICENSE_HEADER}}}
-// {{{ICINGA_LICENSE_HEADER}}}
-
-namespace Icinga\Web\Form\Decorator;
-
-use Zend_Form_Decorator_Abstract;
-
-/**
- * Decorator that automatically adds a helptext to an input element
- * when the 'helptext' attribute is set
- */
-class HelpText extends Zend_Form_Decorator_Abstract
-{
-    /**
-     * Add a helptext to an input field
-     *
-     * @param   string $content The help text
-     *
-     * @return  string The generated tag
-     */
-    public function render($content = '')
-    {
-        $attributes = $this->getElement()->getAttribs();
-        $visible = true;
-        if (isset($attributes['condition'])) {
-            $visible = $attributes['condition'] == '1';
-        }
-        if (isset($attributes['helptext']) && $visible) {
-            $content =  $content
-                . '<p class="help-block">'
-                . $attributes['helptext']
-                . '</p>';
-        }
-        return $content;
-    }
-}