refactor: update registration css and html

Update `Registration.css` and `Registration.html` to enhance UI design. Added a new css class
`.quiqqer-frontendUsers-controls-registrars-list` with properties for flex display, direction, gap,
and width. This class was applied in `Registration.html` to improve the layout of `registrars`
section. Also, removed an unnecessary line in `Registration.php`.

bin/frontend/controls/Registration.css

@@ -34,6 +34,13 @@
     top: -15px;
 }
 
+.quiqqer-frontendUsers-controls-registrars-list {
+    display: flex;
+    flex-direction: column;
+    gap: 0.5rem;
+    width: 100%;
+}
+
 .quiqqer-frontendUsers-controls-registration .quiqqer-frontend-social-button {
     width: 100%;
 }

src/QUI/FrontendUsers/Controls/Registration.html

@@ -94,6 +94,7 @@
             </div>
             {/if}
 
+            <div class="quiqqer-frontendUsers-controls-registrars-list">
             {foreach $registrars as $registrar}
             <form action=""
                   method="POST"
@@ -113,6 +114,7 @@
                 <input type="hidden" name="registration_id" value="{$registrationId}"/>
             </form>
             {/foreach}
+            </div>
 
             {if $termsOfUseRequired}
             <div class="quiqqer-frontendUsers-controls-registration-termsOfUse"

src/QUI/FrontendUsers/Controls/Registration.php

@@ -70,9 +70,7 @@ public function __construct(array $attributes = [])
         ]);
 
         $this->setAttributes($attributes);
-
         $this->setJavaScriptControlOption('registrars', json_encode($this->getAttribute('registrars')));
-        $this->addCSSFile(dirname(__FILE__) . '/Registration.css');
 
         $this->id = QUI\FrontendUsers\Handler::getInstance()->createRegistrationId();
         $this->isAsync = $this->getAttribute('async');