renderjs_ui: do not use placeholder text for login and password

To me, it seems a bit strange from user experience point of view to have suggestions for what login / password to use.

/reviewed-on !67

bt5/erp5_web_renderjs_ui/SkinTemplateItem/portal_skins/erp5_web_renderjs_ui/WebSite_viewRecoverAccount.zpt

@@ -30,7 +30,7 @@
           <form class="login-form" method="post" tal:attributes="action python: context.absolute_url()">
             <div class="ui-field-contain">
               <label data-i18n="Login">Login<span></span></label>
-              <div class="ui-input-text ui-body-inherit ui-corner-all ui-shadow-inset"><input autofocus type="text" name="user_login" placeholder="Ex: john" value="" required=""></div>
+              <div class="ui-input-text ui-body-inherit ui-corner-all ui-shadow-inset"><input autofocus type="text" name="user_login" value="" required=""></div>
             </div>
             <br/>
             <div class="ui-btn ui-input-btn ui-btn-b ui-corner-all ui-shadow ui-btn-inline">Validate<input data-theme="b" data-inline="true" type="submit" data-i18n="[value]Validate" value="Validate" data-icon="check" tal:attributes="name python: '%s:method' % (form_action, )"/></div>

bt5/erp5_web_renderjs_ui/SkinTemplateItem/portal_skins/erp5_web_renderjs_ui/WebSite_viewResetPassword.zpt

@@ -30,11 +30,11 @@
           <form class="login-form" method="post" tal:attributes="action python: context.absolute_url()">
             <div class="ui-field-contain">
               <label data-i18n="New Password">New Password<span></span></label>
-              <div class="ui-input-text ui-body-inherit ui-corner-all ui-shadow-inset"><input autofocus name="password" type="password" placeholder="Ex: A1bcF$99" value="" required=""></div>
+              <div class="ui-input-text ui-body-inherit ui-corner-all ui-shadow-inset"><input autofocus name="password" type="password" value="" required=""></div>
             </div>
             <div class="ui-field-contain">
               <label data-i18n="Retype New Password">Retype New Password<span></span></label>
-              <div class="ui-input-text ui-body-inherit ui-corner-all ui-shadow-inset"><input name="password_confirm" type="password" placeholder="Ex: A1bcF$99" value="" required=""></div>
+              <div class="ui-input-text ui-body-inherit ui-corner-all ui-shadow-inset"><input name="password_confirm" type="password" value="" required=""></div>
             </div>
             <div class="ui-btn ui-input-btn ui-btn-b ui-corner-all ui-shadow ui-btn-inline">Validate<input data-theme="b" data-inline="true" type="submit" data-i18n="[value]Validate" value="Validate" data-icon="check" tal:attributes="name python: '%s:method' % (form_action, )"/></div>
             <input type="hidden" name="came_from" tal:attributes="value python: context.absolute_url()" />

bt5/erp5_web_renderjs_ui/SkinTemplateItem/portal_skins/erp5_web_renderjs_ui/login_form.zpt

@@ -43,11 +43,11 @@
 
             <div class="ui-field-contain">
               <label data-i18n="Login">Login<span></span></label>
-              <div class="ui-input-text ui-body-inherit ui-corner-all ui-shadow-inset"><input autofocus type="text" name="__ac_name" placeholder="Ex: john" value="" required=""></div>
+              <div class="ui-input-text ui-body-inherit ui-corner-all ui-shadow-inset"><input autofocus type="text" name="__ac_name" value="" required=""></div>
             </div>
             <div class="ui-field-contain">
               <label data-i18n="Password">Password<span></span></label>
-              <div class="ui-input-text ui-body-inherit ui-corner-all ui-shadow-inset"><input type="password" name="__ac_password" placeholder="Ex: A1bcF$99" value="" required=""></div>
+              <div class="ui-input-text ui-body-inherit ui-corner-all ui-shadow-inset"><input type="password" name="__ac_password" value="" required=""></div>
             </div>
             <div class="ui-field-contain">
               <label></label>