Don't remove read articles from Unread list

Revert back old behavior (incorrect but, perhaps, more user-friendly),
when Unread list populates with "unread" articles only but then it can
contain "read" articles if they become "read" when Unread list is shown.

src/gui/rss/articlelistwidget.cpp

@@ -93,14 +93,9 @@ void ArticleListWidget::handleArticleAdded(RSS::Article *rssArticle)
 
 void ArticleListWidget::handleArticleRead(RSS::Article *rssArticle)
 {
-    if (m_unreadOnly) {
-        delete m_rssArticleToListItemMapping.take(rssArticle);
-    }
-    else {
-        auto item = mapRSSArticle(rssArticle);
-        item->setData(Qt::ForegroundRole, QColor("grey"));
-        item->setData(Qt::DecorationRole, QIcon(":/icons/sphere.png"));
-    }
+    auto item = mapRSSArticle(rssArticle);
+    item->setData(Qt::ForegroundRole, QColor("grey"));
+    item->setData(Qt::DecorationRole, QIcon(":/icons/sphere.png"));
 
     checkInvariant();
 }