ProjectExplorer: Prevent target switch on project that's to be removed

Switching targets starts up a lot of machinery that is undesired for a
project that's going away.
The same goes for switching build configurations on a target that is
being removed.

Fixes: QTCREATORBUG-25655
Change-Id: I0cb6e395cca8f89bfeb70fcdf571bbcb64f94247
Reviewed-by: hjk <hjk@qt.io>
Reviewed-by: Qt CI Bot <qt_ci_bot@qt-project.org>

src/plugins/genericprojectmanager/genericproject.h

@@ -43,6 +43,7 @@ public:
 private:
     RestoreResult fromMap(const QVariantMap &map, QString *errorMessage) final;
     ProjectExplorer::DeploymentKnowledge deploymentKnowledge() const final;
+    void configureAsExampleProject(ProjectExplorer::Kit *kit) override;
 };
 
 } // namespace Internal