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 nexedi/erp5!67
(cherry picked from commit 8fa68aa9)

Conflicts:
	bt5/erp5_web_renderjs_ui/SkinTemplateItem/portal_skins/erp5_web_renderjs_ui/WebSite_viewRecoverAccount.zpt
	bt5/erp5_web_renderjs_ui/SkinTemplateItem/portal_skins/erp5_web_renderjs_ui/WebSite_viewResetPassword.zpt
	bt5/erp5_web_renderjs_ui/SkinTemplateItem/portal_skins/erp5_web_renderjs_ui/login_form.zpt

bt5/erp5_web_renderjs_ui/SkinTemplateItem/portal_skins/erp5_web_renderjs_ui/WebSite_viewRecoverAccount.xml

@@ -68,7 +68,7 @@
           <form class="login-form" method="post" tal:attributes="action python: context.absolute_url()">\n
             <div class="ui-field-contain">\n
               <label data-i18n="Login">Login<span></span></label>\n
-              <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>\n
+              <div class="ui-input-text ui-body-inherit ui-corner-all ui-shadow-inset"><input autofocus type="text" name="user_login" value="" required=""></div>\n
             </div>\n
             <br/>\n
             <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>\n

bt5/erp5_web_renderjs_ui/SkinTemplateItem/portal_skins/erp5_web_renderjs_ui/WebSite_viewResetPassword.xml

@@ -68,11 +68,11 @@
           <form class="login-form" method="post" tal:attributes="action python: context.absolute_url()">\n
             <div class="ui-field-contain">\n
               <label data-i18n="New Password">New Password<span></span></label>\n
-              <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>\n
+              <div class="ui-input-text ui-body-inherit ui-corner-all ui-shadow-inset"><input autofocus name="password" type="password" value="" required=""></div>\n
             </div>\n
             <div class="ui-field-contain">\n
               <label data-i18n="Retype New Password">Retype New Password<span></span></label>\n
-              <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>\n
+              <div class="ui-input-text ui-body-inherit ui-corner-all ui-shadow-inset"><input name="password_confirm" type="password" value="" required=""></div>\n
             </div>\n
             <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>\n
             <input type="hidden" name="came_from" tal:attributes="value python: context.absolute_url()" />\n

bt5/erp5_web_renderjs_ui/SkinTemplateItem/portal_skins/erp5_web_renderjs_ui/login_form.xml

@@ -81,11 +81,11 @@
 \n
             <div class="ui-field-contain">\n
               <label data-i18n="Login">Login<span></span></label>\n
-              <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>\n
+              <div class="ui-input-text ui-body-inherit ui-corner-all ui-shadow-inset"><input autofocus type="text" name="__ac_name" value="" required=""></div>\n
             </div>\n
             <div class="ui-field-contain">\n
               <label data-i18n="Password">Password<span></span></label>\n
-              <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>\n
+              <div class="ui-input-text ui-body-inherit ui-corner-all ui-shadow-inset"><input type="password" name="__ac_password" value="" required=""></div>\n
             </div>\n
             <div class="ui-field-contain">\n
               <label></label>\n