Remove unused ID (caused duplicates in ChoiceAuth context).

themes/bootstrap3/templates/Auth/AbstractBase/login.phtml

 <? $account = $this->auth()->getManager(); ?>
 <? $sessionInitiator = $account->getSessionInitiator($this->serverUrl($this->url('myresearch-home'))); ?>
 <? if (!$sessionInitiator): // display default login form if no login URL provided ?>
-  <form method="post" class="form-horizontal" action="<?=$this->url('myresearch-home')?>" name="loginForm" id="loginForm">
+  <form method="post" class="form-horizontal" action="<?=$this->url('myresearch-home')?>" name="loginForm">
     <?=$this->auth()->getLoginFields()?>
     <input type="hidden" name="auth_method" value="<?=$account->getAuthMethod()?>">
     <input type="hidden" name="csrf" value="<?=$this->escapeHtmlAttr($account->getCsrfHash(true))?>" />