CMake: Remove dead member from CMakeBuildSystem

Change-Id: Iffdc3d67c2309c1cdc427b383c023d8c98eac037
Reviewed-by: Alessandro Portale <alessandro.portale@qt.io>

src/plugins/cmakeprojectmanager/cmakebuildsystem.h

@@ -101,7 +101,6 @@ private:
     void handleParsingSucceeded();
     void handleParsingFailed(const QString &msg);
 
-    CMakeBuildConfiguration *m_buildConfiguration = nullptr;
     BuildDirManager m_buildDirManager;
 
     ProjectExplorer::TreeScanner m_treeScanner;