Use setPlaceholderText for profile name instead of kmessagewidget

The kmessagewidget was in the wrong location; instead of fixing that
just remove it in favor of using setPlaceholderText.  The only way to
empty the profile name is from user interaction.

See https://phabricator.kde.org/D12523 for comments

src/EditProfileDialog.cpp

@@ -329,23 +329,16 @@ void EditProfileDialog::setupGeneralPage(const Profile::Ptr profile)
 {
     // basic profile options
     {
-        _ui->emptyNameWarningWidget->setWordWrap(false);
-        _ui->emptyNameWarningWidget->setCloseButtonVisible(false);
-        _ui->emptyNameWarningWidget->setMessageType(KMessageWidget::Warning);
+        _ui->profileNameEdit->setPlaceholderText(i18nc("@label:textbox", "Enter descriptive label"));
 
         ProfileGroup::Ptr group = profile->asGroup();
         if (!group || group->profiles().count() < 2) {
             _ui->profileNameEdit->setText(profile->name());
             _ui->profileNameEdit->setClearButtonEnabled(true);
-
-            _ui->emptyNameWarningWidget->setVisible(profile->name().isEmpty());
-            _ui->emptyNameWarningWidget->setText(i18n("Profile name is empty."));
         } else {
             _ui->profileNameEdit->setText(groupProfileNames(group, -1));
             _ui->profileNameEdit->setEnabled(false);
             _ui->profileNameLabel->setEnabled(false);
-
-            _ui->emptyNameWarningWidget->setVisible(false);
         }
     }
 
@@ -491,8 +484,6 @@ void EditProfileDialog::selectIcon()
 
 void EditProfileDialog::profileNameChanged(const QString &name)
 {
-    _ui->emptyNameWarningWidget->setVisible(name.isEmpty());
-
     updateTempProfileProperty(Profile::Name, name);
     updateTempProfileProperty(Profile::UntranslatedName, name);
     updateCaption(_tempProfile);

src/EditProfileDialog.ui

@@ -122,9 +122,6 @@
             </item>
            </layout>
           </item>
-          <item row="1" column="1">
-           <widget class="KMessageWidget" name="emptyNameWarningWidget"/>
-          </item>
           <item row="2" column="0">
            <widget class="QLabel" name="label_3">
             <property name="text">