CppTools: Use Qt5-style connects

Mostly done by clazy.

Change-Id: I0fbbbe1a2d28b79bcb83093d608bca6e2f927ebb
Reviewed-by: Nikolai Kosjar <nikolai.kosjar@qt.io>

src/plugins/cpptools/stringtable.h

@@ -45,11 +45,10 @@ public:
     QString insert(const QString &string);
     void scheduleGC();
 
-private slots:
-    void startGC();
-
 private:
+    void startGC();
     void GC();
+
     class GCRunner: public QRunnable {
         StringTable &m_stringTable;