Cvs: Remove CvsPluginPrivate::cvsVersionControl

Base implementation is good enough.

Change-Id: I9c608f5636a8b9d34375f9c8d690f9c90120c880
Reviewed-by: Eike Ziller <eike.ziller@qt.io>

src/plugins/cvs/cvsplugin.h

@@ -144,7 +144,6 @@ private:
     void startCommit(const QString &workingDir, const QString &file = QString());
     bool commit(const QString &messageFile, const QStringList &subVersionFileList);
     void cleanCommitMessageFile();
-    inline CvsControl *cvsVersionControl() const;
 
     CvsSettings m_settings;
     CvsClient *m_client = nullptr;