qt: Drop redundant OverviewPage::handleOutOfSyncWarningClicks slot

This change makes a connection directly to the signal that was emitted
in the removed slot.

This commit does not change behavior.

src/qt/overviewpage.h

@@ -65,7 +65,6 @@ private Q_SLOTS:
     void handleTransactionClicked(const QModelIndex &index);
     void updateAlerts(const QString &warnings);
     void updateWatchOnlyLabels(bool showWatchOnly);
-    void handleOutOfSyncWarningClicks();
     void setMonospacedFont(bool use_embedded_font);
 };